diff --git a/core/temporal/src/components/month_day.rs b/core/temporal/src/components/month_day.rs
index 1b06eb17c1a..7c3b261dc14 100644
--- a/core/temporal/src/components/month_day.rs
+++ b/core/temporal/src/components/month_day.rs
@@ -1,10 +1,12 @@
 //! This module implements `MonthDay` and any directly related algorithms.
 
+use std::str::FromStr;
+
 use crate::{
     components::calendar::CalendarSlot,
     iso::{IsoDate, IsoDateSlots},
     options::ArithmeticOverflow,
-    TemporalResult,
+    TemporalError, TemporalResult,
 };
 
 /// The native Rust implementation of `Temporal.PlainMonthDay`
@@ -22,8 +24,8 @@ impl MonthDay {
         Self { iso, calendar }
     }
 
-    #[inline]
     /// Creates a new valid `MonthDay`.
+    #[inline]
     pub fn new(
         month: i32,
         day: i32,
@@ -34,9 +36,23 @@ impl MonthDay {
         Ok(Self::new_unchecked(iso, calendar))
     }
 
+    /// Returns the `month` value of `MonthDay`.
     #[inline]
     #[must_use]
+    pub fn month(&self) -> u8 {
+        self.iso.month()
+    }
+
+    /// Returns the `day` value of `MonthDay`.
+    #[inline]
+    #[must_use]
+    pub fn day(&self) -> u8 {
+        self.iso.day()
+    }
+
     /// Returns a reference to `MonthDay`'s `CalendarSlot`
+    #[inline]
+    #[must_use]
     pub fn calendar(&self) -> &CalendarSlot {
         &self.calendar
     }
@@ -49,3 +65,20 @@ impl IsoDateSlots for MonthDay {
         self.iso
     }
 }
+
+impl FromStr for MonthDay {
+    type Err = TemporalError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let record = crate::parser::parse_month_day(s)?;
+
+        let calendar = record.calendar.unwrap_or("iso8601".into());
+
+        Self::new(
+            record.date.month,
+            record.date.day,
+            CalendarSlot::Identifier(calendar),
+            ArithmeticOverflow::Reject,
+        )
+    }
+}
diff --git a/core/temporal/src/components/year_month.rs b/core/temporal/src/components/year_month.rs
index 96e36d6f74d..be9b912a7fe 100644
--- a/core/temporal/src/components/year_month.rs
+++ b/core/temporal/src/components/year_month.rs
@@ -1,10 +1,12 @@
 //! This module implements `YearMonth` and any directly related algorithms.
 
+use std::str::FromStr;
+
 use crate::{
     components::calendar::CalendarSlot,
     iso::{IsoDate, IsoDateSlots},
     options::ArithmeticOverflow,
-    TemporalResult,
+    TemporalError, TemporalResult,
 };
 
 /// The native Rust implementation of `Temporal.YearMonth`.
@@ -36,6 +38,20 @@ impl YearMonth {
         Ok(Self::new_unchecked(iso, calendar))
     }
 
+    /// Returns the `year` value for this `YearMonth`.
+    #[inline]
+    #[must_use]
+    pub fn year(&self) -> i32 {
+        self.iso.year()
+    }
+
+    /// Returns the `month` value for this `YearMonth`.
+    #[inline]
+    #[must_use]
+    pub fn month(&self) -> u8 {
+        self.iso.month()
+    }
+
     #[inline]
     #[must_use]
     /// Returns a reference to `YearMonth`'s `CalendarSlot`
@@ -51,3 +67,21 @@ impl IsoDateSlots for YearMonth {
         self.iso
     }
 }
+
+impl FromStr for YearMonth {
+    type Err = TemporalError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let record = crate::parser::parse_year_month(s)?;
+
+        let calendar = record.calendar.unwrap_or("iso8601".into());
+
+        Self::new(
+            record.date.year,
+            record.date.month,
+            None,
+            CalendarSlot::Identifier(calendar),
+            ArithmeticOverflow::Reject,
+        )
+    }
+}
diff --git a/core/temporal/src/parser/annotations.rs b/core/temporal/src/parser/annotations.rs
index 37e9c7d27e4..50785bf5f4f 100644
--- a/core/temporal/src/parser/annotations.rs
+++ b/core/temporal/src/parser/annotations.rs
@@ -1,5 +1,6 @@
 /// Parsing for Temporal's `Annotations`.
 use crate::{
+    assert_syntax,
     parser::{
         grammar::{
             is_a_key_char, is_a_key_leading_char, is_annotation_close,
@@ -38,10 +39,10 @@ pub(crate) fn parse_annotation_set(
 ) -> TemporalResult<AnnotationSet> {
     // Parse the first annotation.
     let tz_annotation = time_zone::parse_ambiguous_tz_annotation(cursor)?;
-
     if tz_annotation.is_none() && zoned {
-        return Err(TemporalError::syntax()
-            .with_message("iso8601 ZonedDateTime requires a TimeZoneAnnotation."));
+        return Err(
+            TemporalError::syntax().with_message("ZonedDateTime must have a TimeZone annotation.")
+        );
     }
 
     // Parse any `Annotations`
@@ -97,32 +98,27 @@ pub(crate) fn parse_annotations(cursor: &mut Cursor) -> TemporalResult<Recognize
 
 /// Parse an annotation with an `AnnotationKey`=`AnnotationValue` pair.
 fn parse_kv_annotation(cursor: &mut Cursor) -> TemporalResult<KeyValueAnnotation> {
-    debug_assert!(cursor.check_or(false, is_annotation_open));
-
-    let potential_critical = cursor.next().ok_or_else(TemporalError::abrupt_end)?;
-    let (leading_char, critical) = if is_critical_flag(potential_critical) {
-        (cursor.next().ok_or_else(TemporalError::abrupt_end)?, true)
-    } else {
-        (potential_critical, false)
-    };
+    assert_syntax!(
+        is_annotation_open(cursor.abrupt_next()?),
+        "Invalid annotation open character."
+    );
 
-    if !is_a_key_leading_char(leading_char) {
-        return Err(TemporalError::syntax().with_message("Invalid AnnotationKey leading character"));
-    }
+    let critical = cursor.check_or(false, is_critical_flag);
+    cursor.advance_if(critical);
 
     // Parse AnnotationKey.
     let annotation_key = parse_annotation_key(cursor)?;
-
-    debug_assert!(cursor.check_or(false, is_annotation_key_value_separator));
-    // Advance past the '=' character.
-    cursor.advance();
+    assert_syntax!(
+        is_annotation_key_value_separator(cursor.abrupt_next()?),
+        "Invalid annotation key-value separator"
+    );
 
     // Parse AnnotationValue.
     let annotation_value = parse_annotation_value(cursor)?;
-
-    // Assert that we are at the annotation close and advance cursor past annotation to close.
-    debug_assert!(cursor.check_or(false, is_annotation_close));
-    cursor.advance();
+    assert_syntax!(
+        is_annotation_close(cursor.abrupt_next()?),
+        "Invalid annotion closing character"
+    );
 
     Ok(KeyValueAnnotation {
         key: annotation_key,
@@ -134,16 +130,22 @@ fn parse_kv_annotation(cursor: &mut Cursor) -> TemporalResult<KeyValueAnnotation
 /// Parse an `AnnotationKey`.
 fn parse_annotation_key(cursor: &mut Cursor) -> TemporalResult<String> {
     let key_start = cursor.pos();
+    assert_syntax!(
+        is_a_key_leading_char(cursor.abrupt_next()?),
+        "Invalid key leading character."
+    );
+
     while let Some(potential_key_char) = cursor.next() {
         // End of key.
-        if is_annotation_key_value_separator(potential_key_char) {
+        if cursor.check_or(false, is_annotation_key_value_separator) {
             // Return found key
             return Ok(cursor.slice(key_start, cursor.pos()));
         }
 
-        if !is_a_key_char(potential_key_char) {
-            return Err(TemporalError::syntax().with_message("Invalid AnnotationKey Character"));
-        }
+        assert_syntax!(
+            is_a_key_char(potential_key_char),
+            "Invalid annotation key character."
+        );
     }
 
     Err(TemporalError::abrupt_end())
@@ -152,29 +154,26 @@ fn parse_annotation_key(cursor: &mut Cursor) -> TemporalResult<String> {
 /// Parse an `AnnotationValue`.
 fn parse_annotation_value(cursor: &mut Cursor) -> TemporalResult<String> {
     let value_start = cursor.pos();
+    cursor.advance();
     while let Some(potential_value_char) = cursor.next() {
-        if is_annotation_close(potential_value_char) {
+        if cursor.check_or(false, is_annotation_close) {
             // Return the determined AnnotationValue.
             return Ok(cursor.slice(value_start, cursor.pos()));
         }
 
         if is_hyphen(potential_value_char) {
-            if !cursor
-                .peek_n(1)
-                .map_or(false, is_annotation_value_component)
-            {
-                return Err(TemporalError::syntax()
-                    .with_message("Missing AttributeValueComponent after '-'"));
-            }
+            assert_syntax!(
+                cursor.peek().map_or(false, is_annotation_value_component),
+                "Missing annotation value compoenent after '-'"
+            );
             cursor.advance();
             continue;
         }
 
-        if !is_annotation_value_component(potential_value_char) {
-            return Err(
-                TemporalError::syntax().with_message("Invalid character in AnnotationValue")
-            );
-        }
+        assert_syntax!(
+            is_annotation_value_component(potential_value_char),
+            "Invalid annotation value component character."
+        );
     }
 
     Err(TemporalError::abrupt_end())
diff --git a/core/temporal/src/parser/date_time.rs b/core/temporal/src/parser/datetime.rs
similarity index 69%
rename from core/temporal/src/parser/date_time.rs
rename to core/temporal/src/parser/datetime.rs
index 5405e925e86..8061257373c 100644
--- a/core/temporal/src/parser/date_time.rs
+++ b/core/temporal/src/parser/datetime.rs
@@ -1,6 +1,7 @@
 //! Parsing for Temporal's ISO8601 `Date` and `DateTime`.
 
 use crate::{
+    assert_syntax,
     parser::{
         annotations,
         grammar::{is_date_time_separator, is_sign, is_utc_designator},
@@ -67,13 +68,14 @@ pub(crate) fn parse_annotated_date_time(
 
     // Peek Annotation presence
     // Throw error if annotation does not exist and zoned is true, else return.
-    let annotation_check = cursor.check_or(false, is_annotation_open);
-    if !annotation_check {
+    if !cursor.check_or(false, is_annotation_open) {
         if flags.contains(DateTimeFlags::ZONED) {
             return Err(TemporalError::syntax()
                 .with_message("ZonedDateTime must have a TimeZoneAnnotation."));
         }
 
+        cursor.close()?;
+
         return Ok(IsoParseRecord {
             date: date_time.date,
             time: date_time.time,
@@ -101,6 +103,8 @@ pub(crate) fn parse_annotated_date_time(
         None
     };
 
+    cursor.close()?;
+
     Ok(IsoParseRecord {
         date: date_time.date,
         time: date_time.time,
@@ -134,10 +138,7 @@ fn parse_date_time(
 
     let time = time::parse_time_spec(cursor)?;
 
-    let time_zone = if cursor
-        .check(|ch| is_sign(ch) || is_utc_designator(ch))
-        .unwrap_or(false)
-    {
+    let time_zone = if cursor.check_or(false, |ch| is_sign(ch) || is_utc_designator(ch)) {
         Some(time_zone::parse_date_time_utc(cursor)?)
     } else {
         if utc_required {
@@ -156,93 +157,40 @@ fn parse_date_time(
 /// Parses `Date` record.
 fn parse_date(cursor: &mut Cursor) -> TemporalResult<DateRecord> {
     let year = parse_date_year(cursor)?;
-    let divided = cursor
+    let hyphenated = cursor
         .check(is_hyphen)
         .ok_or_else(TemporalError::abrupt_end)?;
 
-    if divided {
-        cursor.advance();
-    }
+    cursor.advance_if(hyphenated);
 
     let month = parse_date_month(cursor)?;
 
-    if cursor.check_or(false, is_hyphen) {
-        if !divided {
-            return Err(TemporalError::syntax().with_message("Invalid date separator"));
-        }
-        cursor.advance();
+    if hyphenated {
+        assert_syntax!(cursor.check_or(false, is_hyphen), "Invalid hyphen usage.");
     }
+    cursor.advance_if(cursor.check_or(false, is_hyphen));
 
     let day = parse_date_day(cursor)?;
 
     Ok(DateRecord { year, month, day })
 }
 
-/// Determines if the string can be parsed as a `DateSpecYearMonth`.
-pub(crate) fn peek_year_month(cursor: &Cursor) -> TemporalResult<bool> {
-    let mut ym_peek = if is_sign(cursor.peek().ok_or_else(TemporalError::abrupt_end)?) {
-        7
-    } else {
-        4
-    };
-
-    if cursor
-        .peek_n(ym_peek)
-        .map(is_hyphen)
-        .ok_or_else(TemporalError::abrupt_end)?
-    {
-        ym_peek += 1;
-    }
-
-    ym_peek += 2;
-
-    if cursor.peek_n(ym_peek).map_or(true, is_annotation_open) {
-        Ok(true)
-    } else {
-        Ok(false)
-    }
-}
+// ==== `YearMonth` and `MonthDay` parsing functions ====
 
 /// Parses a `DateSpecYearMonth`
 pub(crate) fn parse_year_month(cursor: &mut Cursor) -> TemporalResult<(i32, i32)> {
     let year = parse_date_year(cursor)?;
 
-    if cursor.check_or(false, is_hyphen) {
-        cursor.advance();
-    }
+    cursor.advance_if(cursor.check_or(false, is_hyphen));
 
     let month = parse_date_month(cursor)?;
 
-    Ok((year, month))
-}
-
-/// Determines if the string can be parsed as a `DateSpecYearMonth`.
-pub(crate) fn peek_month_day(cursor: &Cursor) -> TemporalResult<bool> {
-    let mut md_peek = if cursor
-        .peek_n(1)
-        .map(is_hyphen)
-        .ok_or_else(TemporalError::abrupt_end)?
-    {
-        4
-    } else {
-        2
-    };
-
-    if cursor
-        .peek_n(md_peek)
-        .map(is_hyphen)
-        .ok_or_else(TemporalError::abrupt_end)?
-    {
-        md_peek += 1;
-    }
-
-    md_peek += 2;
+    assert_syntax!(
+        cursor.check_or(true, is_annotation_open),
+        "Expected an end or AnnotationOpen"
+    );
 
-    if cursor.peek_n(md_peek).map_or(true, is_annotation_open) {
-        Ok(true)
-    } else {
-        Ok(false)
-    }
+    Ok((year, month))
 }
 
 /// Parses a `DateSpecMonthDay`
@@ -251,7 +199,7 @@ pub(crate) fn parse_month_day(cursor: &mut Cursor) -> TemporalResult<(i32, i32)>
         .check(is_hyphen)
         .ok_or_else(TemporalError::abrupt_end)?;
     let dash_two = cursor
-        .peek_n(1)
+        .peek()
         .map(is_hyphen)
         .ok_or_else(TemporalError::abrupt_end)?;
 
@@ -262,38 +210,36 @@ pub(crate) fn parse_month_day(cursor: &mut Cursor) -> TemporalResult<(i32, i32)>
     }
 
     let month = parse_date_month(cursor)?;
-    if cursor.check_or(false, is_hyphen) {
-        cursor.advance();
-    }
+
+    cursor.advance_if(cursor.check_or(false, is_hyphen));
 
     let day = parse_date_day(cursor)?;
 
+    assert_syntax!(
+        cursor.check_or(true, is_annotation_open),
+        "Expected an end or AnnotationOpen"
+    );
+
     Ok((month, day))
 }
 
 // ==== Unit Parsers ====
 
 fn parse_date_year(cursor: &mut Cursor) -> TemporalResult<i32> {
-    if is_sign(cursor.peek().ok_or_else(TemporalError::abrupt_end)?) {
+    if cursor.check_or(false, is_sign) {
+        let sign = if cursor.expect_next() == '+' { 1 } else { -1 };
         let year_start = cursor.pos();
-        let sign = if cursor.check_or(false, |ch| ch == '+') {
-            1
-        } else {
-            -1
-        };
-
-        cursor.advance();
 
         for _ in 0..6 {
-            let year_digit = cursor.peek().ok_or_else(TemporalError::abrupt_end)?;
-            if !year_digit.is_ascii_digit() {
-                return Err(TemporalError::syntax().with_message("DateYear must contain digit"));
-            }
-            cursor.advance();
+            let year_digit = cursor.abrupt_next()?;
+            assert_syntax!(
+                year_digit.is_ascii_digit(),
+                "Year must be made up of digits."
+            );
         }
 
-        let year_string = cursor.slice(year_start + 1, cursor.pos());
-        let year_value = year_string
+        let year_value = cursor
+            .slice(year_start, cursor.pos())
             .parse::<i32>()
             .map_err(|e| TemporalError::syntax().with_message(e.to_string()))?;
 
@@ -304,21 +250,28 @@ fn parse_date_year(cursor: &mut Cursor) -> TemporalResult<i32> {
             return Err(TemporalError::syntax().with_message("Cannot have negative 0 years."));
         }
 
-        return Ok(sign * year_value);
+        let year = sign * year_value;
+
+        if !(-271_820..=275_760).contains(&year) {
+            return Err(TemporalError::range()
+                .with_message("Year is outside of the minimum supported range."));
+        }
+
+        return Ok(year);
     }
 
     let year_start = cursor.pos();
 
     for _ in 0..4 {
-        let year_digit = cursor.peek().ok_or_else(TemporalError::abrupt_end)?;
-        if !year_digit.is_ascii_digit() {
-            return Err(TemporalError::syntax().with_message("DateYear must contain digit"));
-        }
-        cursor.advance();
+        let year_digit = cursor.abrupt_next()?;
+        assert_syntax!(
+            year_digit.is_ascii_digit(),
+            "Year must be made up of digits."
+        );
     }
 
-    let year_string = cursor.slice(year_start, cursor.pos());
-    let year_value = year_string
+    let year_value = cursor
+        .slice(year_start, cursor.pos())
         .parse::<i32>()
         .map_err(|e| TemporalError::syntax().with_message(e.to_string()))?;
 
@@ -326,25 +279,33 @@ fn parse_date_year(cursor: &mut Cursor) -> TemporalResult<i32> {
 }
 
 fn parse_date_month(cursor: &mut Cursor) -> TemporalResult<i32> {
+    let start = cursor.pos();
+    for _ in 0..2 {
+        let digit = cursor.abrupt_next()?;
+        assert_syntax!(digit.is_ascii_digit(), "Month must be a digit");
+    }
     let month_value = cursor
-        .slice(cursor.pos(), cursor.pos() + 2)
+        .slice(start, cursor.pos())
         .parse::<i32>()
         .map_err(|e| TemporalError::syntax().with_message(e.to_string()))?;
     if !(1..=12).contains(&month_value) {
         return Err(TemporalError::syntax().with_message("DateMonth must be in a range of 1-12"));
     }
-    cursor.advance_n(2);
     Ok(month_value)
 }
 
 fn parse_date_day(cursor: &mut Cursor) -> TemporalResult<i32> {
+    let start = cursor.pos();
+    for _ in 0..2 {
+        let digit = cursor.abrupt_next()?;
+        assert_syntax!(digit.is_ascii_digit(), "Date must be a digit");
+    }
     let day_value = cursor
-        .slice(cursor.pos(), cursor.pos() + 2)
+        .slice(start, cursor.pos())
         .parse::<i32>()
         .map_err(|e| TemporalError::syntax().with_message(e.to_string()))?;
     if !(1..=31).contains(&day_value) {
         return Err(TemporalError::syntax().with_message("DateDay must be in a range of 1-31"));
     }
-    cursor.advance_n(2);
     Ok(day_value)
 }
diff --git a/core/temporal/src/parser/duration.rs b/core/temporal/src/parser/duration.rs
index 3d9421e04f0..10d182fcc28 100644
--- a/core/temporal/src/parser/duration.rs
+++ b/core/temporal/src/parser/duration.rs
@@ -1,4 +1,5 @@
 use crate::{
+    assert_syntax,
     parser::{
         grammar::{
             is_day_designator, is_decimal_separator, is_duration_designator, is_hour_designator,
@@ -57,23 +58,15 @@ pub(crate) fn parse_duration(cursor: &mut Cursor) -> TemporalResult<DurationPars
         .check(is_sign)
         .ok_or_else(TemporalError::abrupt_end)?
     {
-        let sign = cursor.check_or(false, |ch| ch == '+');
-        cursor.advance();
-        sign
+        cursor.expect_next() == '+'
     } else {
         true
     };
 
-    if !cursor
-        .check(is_duration_designator)
-        .ok_or_else(TemporalError::abrupt_end)?
-    {
-        return Err(
-            TemporalError::syntax().with_message("DurationString missing DurationDesignator.")
-        );
-    }
-
-    cursor.advance();
+    assert_syntax!(
+        is_duration_designator(cursor.abrupt_next()?),
+        "DurationDisgnator is missing."
+    );
 
     let date = if cursor.check_or(false, is_time_designator) {
         Some(DateDuration::default())
@@ -88,9 +81,7 @@ pub(crate) fn parse_duration(cursor: &mut Cursor) -> TemporalResult<DurationPars
         None
     };
 
-    if cursor.peek().is_some() {
-        return Err(TemporalError::syntax().with_message("Unrecognized value in DurationString."));
-    }
+    cursor.close()?;
 
     Ok(DurationParseRecord {
         sign,
@@ -115,8 +106,10 @@ pub(crate) fn parse_date_duration(cursor: &mut Cursor) -> TemporalResult<DateDur
     while cursor.check_or(false, |ch| ch.is_ascii_digit()) {
         let digit_start = cursor.pos();
 
-        while cursor.check_or(false, |ch| ch.is_ascii_digit()) {
-            cursor.advance();
+        while cursor.next().is_some() {
+            if !cursor.check_or(false, |ch| ch.is_ascii_digit()) {
+                break;
+            }
         }
 
         let value = cursor
@@ -124,7 +117,7 @@ pub(crate) fn parse_date_duration(cursor: &mut Cursor) -> TemporalResult<DateDur
             .parse::<i32>()
             .map_err(|err| TemporalError::syntax().with_message(err.to_string()))?;
 
-        match cursor.peek() {
+        match cursor.next() {
             Some(ch) if is_year_designator(ch) => {
                 if previous_unit > DateUnit::Year {
                     return Err(
@@ -163,8 +156,6 @@ pub(crate) fn parse_date_duration(cursor: &mut Cursor) -> TemporalResult<DateDur
             }
             Some(_) | None => return Err(TemporalError::abrupt_end()),
         }
-
-        cursor.advance();
     }
 
     Ok(date)
@@ -181,19 +172,20 @@ enum TimeUnit {
 pub(crate) fn parse_time_duration(cursor: &mut Cursor) -> TemporalResult<TimeDuration> {
     let mut time = TimeDuration::default();
 
-    if !cursor.check_or(false, |ch| ch.is_ascii()) {
-        return Err(
-            TemporalError::syntax().with_message("No time values provided after TimeDesignator.")
-        );
-    }
+    assert_syntax!(
+        cursor.check_or(false, |ch| ch.is_ascii_digit()),
+        "TimeDuration designator must have values after."
+    );
 
     let mut previous_unit = TimeUnit::None;
     let mut fraction_present = false;
     while cursor.check_or(false, |ch| ch.is_ascii_digit()) {
         let digit_start = cursor.pos();
 
-        while cursor.check_or(false, |ch| ch.is_ascii_digit()) {
-            cursor.advance();
+        while cursor.next().is_some() {
+            if !cursor.check_or(false, |ch| ch.is_ascii_digit()) {
+                break;
+            }
         }
 
         let value = cursor
@@ -208,7 +200,7 @@ pub(crate) fn parse_time_duration(cursor: &mut Cursor) -> TemporalResult<TimeDur
             0.0
         };
 
-        match cursor.peek() {
+        match cursor.next() {
             Some(ch) if is_hour_designator(ch) => {
                 if previous_unit > TimeUnit::Hour {
                     return Err(
@@ -242,14 +234,11 @@ pub(crate) fn parse_time_duration(cursor: &mut Cursor) -> TemporalResult<TimeDur
             Some(_) | None => return Err(TemporalError::abrupt_end()),
         }
 
-        cursor.advance();
-
         if fraction_present {
-            if cursor.check_or(false, |ch| ch.is_ascii_digit()) {
-                return Err(TemporalError::syntax()
-                    .with_message("Invalid TimeDuration continuation after FractionPart."));
-            }
-
+            assert_syntax!(
+                cursor.check_or(true, |ch| !ch.is_ascii_digit()),
+                "Invalid duration value provided after fraction."
+            );
             break;
         }
     }
diff --git a/core/temporal/src/parser/mod.rs b/core/temporal/src/parser/mod.rs
index f9e07fbd8d3..48bfee3ba3a 100644
--- a/core/temporal/src/parser/mod.rs
+++ b/core/temporal/src/parser/mod.rs
@@ -1,40 +1,113 @@
 //! This module implements parsing for ISO 8601 grammar.
 
-use crate::TemporalResult;
+use crate::{TemporalError, TemporalResult};
 
-use date_time::DateRecord;
+use datetime::DateRecord;
 use nodes::{IsoDate, IsoDateTime, IsoTime, TimeZone};
 use time::TimeSpec;
 
 mod annotations;
-pub(crate) mod date_time;
+pub(crate) mod datetime;
 pub(crate) mod duration;
 mod grammar;
 mod nodes;
 mod time;
 pub(crate) mod time_zone;
 
-use self::date_time::DateTimeFlags;
+use self::{datetime::DateTimeFlags, grammar::is_annotation_open};
 
 #[cfg(test)]
 mod tests;
 
 // TODO: optimize where possible.
 
+/// `assert_syntax!` is a parser specific utility macro for asserting a syntax test, and returning a
+/// `SyntaxError` with the provided message if the test fails.
+#[macro_export]
+macro_rules! assert_syntax {
+    ($cond:expr, $msg:literal) => {
+        if !$cond {
+            return Err(TemporalError::syntax().with_message($msg));
+        }
+    };
+}
+
 /// A utility function for parsing a `DateTime` string
 pub(crate) fn parse_date_time(target: &str) -> TemporalResult<IsoParseRecord> {
-    date_time::parse_annotated_date_time(DateTimeFlags::empty(), &mut Cursor::new(target))
+    datetime::parse_annotated_date_time(DateTimeFlags::empty(), &mut Cursor::new(target))
 }
 
 /// A utility function for parsing an `Instant` string
 #[allow(unused)]
 pub(crate) fn parse_instant(target: &str) -> TemporalResult<IsoParseRecord> {
-    date_time::parse_annotated_date_time(
+    datetime::parse_annotated_date_time(
         DateTimeFlags::UTC_REQ | DateTimeFlags::TIME_REQ,
         &mut Cursor::new(target),
     )
 }
 
+/// A utility function for parsing a `YearMonth` string
+pub(crate) fn parse_year_month(target: &str) -> TemporalResult<IsoParseRecord> {
+    let mut cursor = Cursor::new(target);
+    let ym = datetime::parse_year_month(&mut cursor);
+
+    let Ok(year_month) = ym else {
+        cursor.pos = 0;
+        return datetime::parse_annotated_date_time(DateTimeFlags::empty(), &mut cursor);
+    };
+
+    let calendar = if cursor.check_or(false, is_annotation_open) {
+        let set = annotations::parse_annotation_set(false, &mut cursor)?;
+        set.calendar
+    } else {
+        None
+    };
+
+    cursor.close()?;
+
+    Ok(IsoParseRecord {
+        date: DateRecord {
+            year: year_month.0,
+            month: year_month.1,
+            day: 1,
+        },
+        time: None,
+        tz: None,
+        calendar,
+    })
+}
+
+/// A utilty function for parsing a `MonthDay` String.
+pub(crate) fn parse_month_day(target: &str) -> TemporalResult<IsoParseRecord> {
+    let mut cursor = Cursor::new(target);
+    let md = datetime::parse_month_day(&mut cursor);
+
+    let Ok(month_day) = md else {
+        cursor.pos = 0;
+        return datetime::parse_annotated_date_time(DateTimeFlags::empty(), &mut cursor);
+    };
+
+    let calendar = if cursor.check_or(false, is_annotation_open) {
+        let set = annotations::parse_annotation_set(false, &mut cursor)?;
+        set.calendar
+    } else {
+        None
+    };
+
+    cursor.close()?;
+
+    Ok(IsoParseRecord {
+        date: DateRecord {
+            year: 0,
+            month: month_day.0,
+            day: month_day.1,
+        },
+        time: None,
+        tz: None,
+        calendar,
+    })
+}
+
 /// An `IsoParseRecord` is an intermediary record returned by ISO parsing functions.
 ///
 /// `IsoParseRecord` is converted into the ISO AST Nodes.
@@ -70,94 +143,6 @@ impl TemporalTimeZoneString {
     }
 }
 
-/// Parse a [`TemporalYearMonthString`][proposal]
-///
-/// [proposal]: https://tc39.es/proposal-temporal/#prod-TemporalYearMonthString
-#[derive(Debug, Clone, Copy)]
-pub struct TemporalYearMonthString;
-
-impl TemporalYearMonthString {
-    /// Parses a targeted string as a `YearMonth`
-    ///
-    /// # Errors
-    ///
-    /// The parse will error if the provided target is not valid
-    /// Iso8601 grammar.
-    pub fn parse(cursor: &mut Cursor) -> TemporalResult<IsoDate> {
-        // TODO: Remove peek in favor of AnnotatedDateTime flag.
-        if date_time::peek_year_month(cursor)? {
-            let ym = date_time::parse_year_month(cursor)?;
-
-            let calendar = if cursor.check_or(false, |ch| ch == '[') {
-                let set = annotations::parse_annotation_set(false, cursor)?;
-                set.calendar
-            } else {
-                None
-            };
-
-            return Ok(IsoDate {
-                year: ym.0,
-                month: ym.1,
-                day: 0,
-                calendar,
-            });
-        }
-
-        let parse_record = date_time::parse_annotated_date_time(DateTimeFlags::empty(), cursor)?;
-
-        Ok(IsoDate {
-            year: parse_record.date.year,
-            month: parse_record.date.month,
-            day: parse_record.date.day,
-            calendar: parse_record.calendar,
-        })
-    }
-}
-
-/// Parse a [`TemporalMonthDayString`][proposal]
-///
-/// [proposal]: https://tc39.es/proposal-temporal/#prod-TemporalMonthDayString
-#[derive(Debug, Clone, Copy)]
-pub struct TemporalMonthDayString;
-
-impl TemporalMonthDayString {
-    /// Parses a targeted string as a `MonthDay`.
-    ///
-    /// # Errors
-    ///
-    /// The parse will error if the provided target is not valid
-    /// Iso8601 grammar.
-    pub fn parse(cursor: &mut Cursor) -> TemporalResult<IsoDate> {
-        // TODO: Remove peek in favor of AnnotatedDateTime flag.
-        if date_time::peek_month_day(cursor)? {
-            let md = date_time::parse_month_day(cursor)?;
-
-            let calendar = if cursor.check_or(false, |ch| ch == '[') {
-                let set = annotations::parse_annotation_set(false, cursor)?;
-                set.calendar
-            } else {
-                None
-            };
-
-            return Ok(IsoDate {
-                year: 0,
-                month: md.0,
-                day: md.1,
-                calendar,
-            });
-        }
-
-        let parse_record = date_time::parse_annotated_date_time(DateTimeFlags::empty(), cursor)?;
-
-        Ok(IsoDate {
-            year: parse_record.date.year,
-            month: parse_record.date.month,
-            day: parse_record.date.day,
-            calendar: parse_record.calendar,
-        })
-    }
-}
-
 /// Parser for a [`TemporalInstantString`][proposal].
 ///
 /// [proposal]: https://tc39.es/proposal-temporal/#prod-TemporalInstantString
@@ -172,7 +157,7 @@ impl TemporalInstantString {
     /// The parse will error if the provided target is not valid
     /// Iso8601 grammar.
     pub fn parse(cursor: &mut Cursor) -> TemporalResult<IsoDateTime> {
-        let parse_record = date_time::parse_annotated_date_time(
+        let parse_record = datetime::parse_annotated_date_time(
             DateTimeFlags::UTC_REQ | DateTimeFlags::TIME_REQ,
             cursor,
         )?;
@@ -225,13 +210,9 @@ impl Cursor {
         self.pos
     }
 
-    /// Peek the value at the current position.
+    /// Peek the value at next position (current + 1).
     fn peek(&self) -> Option<char> {
-        if (self.pos as usize) < self.source.len() {
-            Some(self.source[self.pos as usize])
-        } else {
-            None
-        }
+        self.peek_n(1)
     }
 
     /// Peek the value at n len from current.
@@ -244,25 +225,41 @@ impl Cursor {
         }
     }
 
-    /// Returns boolean if current position passes check.
+    /// Runs the provided check on the current position.
     fn check<F>(&self, f: F) -> Option<bool>
     where
         F: FnOnce(char) -> bool,
     {
-        self.peek().map(f)
+        self.peek_n(0).map(f)
     }
 
-    /// Returns boolean if current position passes check or default if None.
+    /// Runs the provided check on current position returns the default value if None.
     fn check_or<F>(&self, default: bool, f: F) -> bool
     where
         F: FnOnce(char) -> bool,
     {
-        self.peek().map_or(default, f)
+        self.peek_n(0).map_or(default, f)
     }
-    /// Advances the cursor's position and returns the new character.
+
+    /// Returns `Cursor`'s current char and advances to the next position.
     fn next(&mut self) -> Option<char> {
+        let result = self.peek_n(0);
         self.advance();
-        self.peek()
+        result
+    }
+
+    /// Utility method that returns next charactor unwrapped char
+    ///
+    /// # Panics
+    ///
+    /// This will panic if the next value has not been confirmed to exist.
+    fn expect_next(&mut self) -> char {
+        self.next().expect("Invalid use of expect_next.")
+    }
+
+    /// A utility next method that returns an `AbruptEnd` error if invalid.
+    fn abrupt_next(&mut self) -> TemporalResult<char> {
+        self.next().ok_or_else(TemporalError::abrupt_end)
     }
 
     /// Advances the cursor's position by 1.
@@ -270,8 +267,24 @@ impl Cursor {
         self.pos += 1;
     }
 
+    /// Utility function to advance when a condition is true
+    fn advance_if(&mut self, condition: bool) {
+        if condition {
+            self.advance();
+        }
+    }
+
     /// Advances the cursor's position by `n`.
     fn advance_n(&mut self, n: u32) {
         self.pos += n;
     }
+
+    /// Closes the current cursor by checking if all contents have been consumed. If not, returns an error for invalid syntax.
+    fn close(&mut self) -> TemporalResult<()> {
+        if (self.pos as usize) < self.source.len() {
+            return Err(TemporalError::syntax()
+                .with_message("Unexpected syntax at the end of an ISO target."));
+        }
+        Ok(())
+    }
 }
diff --git a/core/temporal/src/parser/tests.rs b/core/temporal/src/parser/tests.rs
index ef0e18726de..846b720d382 100644
--- a/core/temporal/src/parser/tests.rs
+++ b/core/temporal/src/parser/tests.rs
@@ -1,11 +1,8 @@
 use std::str::FromStr;
 
 use crate::{
-    components::{DateTime, Duration},
-    parser::{
-        parse_date_time, Cursor, TemporalInstantString, TemporalMonthDayString,
-        TemporalYearMonthString,
-    },
+    components::{DateTime, Duration, MonthDay, YearMonth},
+    parser::{parse_date_time, Cursor, TemporalInstantString},
 };
 
 #[test]
@@ -56,7 +53,10 @@ fn temporal_year_parsing() {
     assert_eq!(result_good.iso_date().year(), 2020);
 
     let err_result = bad_year.parse::<DateTime>();
-    assert!(err_result.is_err());
+    assert!(
+        err_result.is_err(),
+        "Invalid extended year parsing: \"{bad_year}\" should fail to parse."
+    );
 }
 
 #[test]
@@ -81,34 +81,37 @@ fn temporal_annotated_date_time() {
 
 #[test]
 fn temporal_year_month() {
-    let possible_year_months = &[
+    let possible_year_months = [
         "+002020-11",
         "2020-11[u-ca=iso8601]",
         "+00202011",
         "202011[u-ca=iso8601]",
+        "+002020-11-07T12:28:32[!u-ca=iso8601]",
     ];
 
     for ym in possible_year_months {
-        let result = TemporalYearMonthString::parse(&mut Cursor::new(ym)).unwrap();
-
-        assert_eq!(result.year, 2020);
-        assert_eq!(result.month, 11);
+        let result = ym.parse::<YearMonth>().unwrap();
 
-        if let Some(calendar) = result.calendar {
-            assert_eq!(calendar, "iso8601");
-        }
+        assert_eq!(result.year(), 2020);
+        assert_eq!(result.month(), 11);
     }
 }
 
 #[test]
 fn temporal_month_day() {
-    let possible_month_day = ["11-07", "1107[+04:00]", "--11-07", "--1107[+04:00]"];
+    let possible_month_day = [
+        "11-07",
+        "1107[+04:00]",
+        "--11-07",
+        "--1107[+04:00]",
+        "+002020-11-07T12:28:32[!u-ca=iso8601]",
+    ];
 
     for md in possible_month_day {
-        let result = TemporalMonthDayString::parse(&mut Cursor::new(md)).unwrap();
+        let result = md.parse::<MonthDay>().unwrap();
 
-        assert_eq!(result.month, 11);
-        assert_eq!(result.day, 7);
+        assert_eq!(result.month(), 11);
+        assert_eq!(result.day(), 7);
     }
 }
 
@@ -121,8 +124,11 @@ fn temporal_invalid_annotations() {
     ];
 
     for invalid in invalid_annotations {
-        let err_result = TemporalMonthDayString::parse(&mut Cursor::new(invalid));
-        assert!(err_result.is_err());
+        let err_result = invalid.parse::<MonthDay>();
+        assert!(
+            err_result.is_err(),
+            "Invalid ISO annotation parsing: \"{invalid}\" should fail parsing."
+        );
     }
 }
 
@@ -153,7 +159,10 @@ fn temporal_duration_parsing() {
 
     for dur in durations {
         let ok_result = Duration::from_str(dur);
-        assert!(ok_result.is_ok());
+        assert!(
+            ok_result.is_ok(),
+            "Failing to parse a valid ISO 8601 target: \"{dur}\" should pass."
+        );
     }
 
     let sub_second = durations[2].parse::<Duration>().unwrap();
@@ -180,6 +189,61 @@ fn temporal_invalid_durations() {
 
     for test in invalids {
         let err = test.parse::<Duration>();
-        assert!(err.is_err());
+        assert!(
+            err.is_err(),
+            "Invalid ISO8601 Duration target: \"{test}\" should fail duration parsing."
+        );
+    }
+}
+
+#[test]
+fn temporal_invalid_iso_datetime_strings() {
+    // NOTE: The below tests were initially pulled from test262's `argument-string-invalid`
+    const INVALID_DATETIME_STRINGS: [&str; 34] = [
+        "", // 1
+        "invalid iso8601",
+        "2020-01-00",
+        "2020-01-32",
+        "2020-02-30",
+        "2021-02-29",
+        "2020-00-01",
+        "2020-13-01",
+        "2020-01-01T",
+        "2020-01-01T25:00:00",
+        "2020-01-01T01:60:00",
+        "2020-01-01T01:60:61",
+        "2020-01-01junk",
+        "2020-01-01T00:00:00junk",
+        "2020-01-01T00:00:00+00:00junk",
+        "2020-01-01T00:00:00+00:00[UTC]junk",
+        "2020-01-01T00:00:00+00:00[UTC][u-ca=iso8601]junk",
+        "02020-01-01",
+        "2020-001-01",
+        "2020-01-001",
+        "2020-01-01T001",
+        "2020-01-01T01:001",
+        "2020-01-01T01:01:001",
+        "2020-W01-1",
+        "2020-001",
+        "+0002020-01-01",
+        // TODO: Add the non-existent calendar test back to the test cases.
+        // may be valid in other contexts, but insufficient information for PlainDate:
+        "2020-01",
+        "+002020-01",
+        "01-01",
+        "2020-W01",
+        "P1Y",
+        "-P12Y",
+        // valid, but outside the supported range:
+        "-999999-01-01",
+        "+999999-01-01",
+    ];
+
+    for invalid_target in INVALID_DATETIME_STRINGS {
+        let error_result = invalid_target.parse::<DateTime>();
+        assert!(
+            error_result.is_err(),
+            "Invalid ISO8601 `DateTime` target: \"{invalid_target}\" should fail parsing."
+        );
     }
 }
diff --git a/core/temporal/src/parser/time.rs b/core/temporal/src/parser/time.rs
index a1f2cec09d2..d58fcbe4591 100644
--- a/core/temporal/src/parser/time.rs
+++ b/core/temporal/src/parser/time.rs
@@ -4,7 +4,7 @@ use super::{
     grammar::{is_decimal_separator, is_time_separator},
     Cursor,
 };
-use crate::{TemporalError, TemporalResult};
+use crate::{assert_syntax, TemporalError, TemporalResult};
 
 /// Parsed Time info
 #[derive(Debug, Default, Clone, Copy)]
@@ -22,14 +22,8 @@ pub(crate) struct TimeSpec {
 /// Parse `TimeSpec`
 pub(crate) fn parse_time_spec(cursor: &mut Cursor) -> TemporalResult<TimeSpec> {
     let hour = parse_hour(cursor)?;
-    let mut separator = false;
 
-    if cursor.check_or(false, |ch| is_time_separator(ch) || ch.is_ascii_digit()) {
-        if cursor.check_or(false, is_time_separator) {
-            separator = true;
-            cursor.advance();
-        }
-    } else {
+    if !cursor.check_or(false, |ch| is_time_separator(ch) || ch.is_ascii_digit()) {
         return Ok(TimeSpec {
             hour,
             minute: 0,
@@ -38,24 +32,24 @@ pub(crate) fn parse_time_spec(cursor: &mut Cursor) -> TemporalResult<TimeSpec> {
         });
     }
 
+    let separator_present = cursor.check_or(false, is_time_separator);
+    cursor.advance_if(separator_present);
+
     let minute = parse_minute_second(cursor, false)?;
 
-    if cursor.check_or(false, |ch| is_time_separator(ch) || ch.is_ascii_digit()) {
-        let is_time_separator = cursor.check_or(false, is_time_separator);
-        if separator && is_time_separator {
-            cursor.advance();
-        } else if is_time_separator {
-            return Err(TemporalError::syntax().with_message("Invalid TimeSeparator"));
-        }
-    } else {
+    if !cursor.check_or(false, |ch| is_time_separator(ch) || ch.is_ascii_digit()) {
         return Ok(TimeSpec {
             hour,
             minute,
             second: 0,
             fraction: 0.0,
         });
+    } else if cursor.check_or(false, is_time_separator) && !separator_present {
+        return Err(TemporalError::syntax().with_message("Invalid TimeSeparator"));
     }
 
+    cursor.advance_if(separator_present);
+
     let second = parse_minute_second(cursor, true)?;
 
     let fraction = if cursor.check_or(false, is_decimal_separator) {
@@ -73,22 +67,31 @@ pub(crate) fn parse_time_spec(cursor: &mut Cursor) -> TemporalResult<TimeSpec> {
 }
 
 pub(crate) fn parse_hour(cursor: &mut Cursor) -> TemporalResult<u8> {
+    let start = cursor.pos();
+    for _ in 0..2 {
+        let digit = cursor.abrupt_next()?;
+        assert_syntax!(digit.is_ascii_digit(), "Hour must be a digit.");
+    }
     let hour_value = cursor
-        .slice(cursor.pos(), cursor.pos() + 2)
+        .slice(start, cursor.pos())
         .parse::<u8>()
         .map_err(|e| TemporalError::syntax().with_message(e.to_string()))?;
     if !(0..=23).contains(&hour_value) {
         return Err(TemporalError::syntax().with_message("Hour must be in a range of 0-23"));
     }
-    cursor.advance_n(2);
     Ok(hour_value)
 }
 
 // NOTE: `TimeSecond` is a 60 inclusive `MinuteSecond`.
 /// Parse `MinuteSecond`
 pub(crate) fn parse_minute_second(cursor: &mut Cursor, inclusive: bool) -> TemporalResult<u8> {
+    let start = cursor.pos();
+    for _ in 0..2 {
+        let digit = cursor.abrupt_next()?;
+        assert_syntax!(digit.is_ascii_digit(), "MinuteSecond must be a digit.");
+    }
     let min_sec_value = cursor
-        .slice(cursor.pos(), cursor.pos() + 2)
+        .slice(start, cursor.pos())
         .parse::<u8>()
         .map_err(|e| TemporalError::syntax().with_message(e.to_string()))?;
 
@@ -96,8 +99,6 @@ pub(crate) fn parse_minute_second(cursor: &mut Cursor, inclusive: bool) -> Tempo
     if !valid_range.contains(&min_sec_value) {
         return Err(TemporalError::syntax().with_message("MinuteSecond must be in a range of 0-59"));
     }
-
-    cursor.advance_n(2);
     Ok(min_sec_value)
 }
 
@@ -106,25 +107,28 @@ pub(crate) fn parse_minute_second(cursor: &mut Cursor, inclusive: bool) -> Tempo
 /// This is primarily used in ISO8601 to add percision past
 /// a second.
 pub(crate) fn parse_fraction(cursor: &mut Cursor) -> TemporalResult<f64> {
-    // Decimal is skipped by next call.
-    let mut fraction_components = Vec::from(['.']);
-    while let Some(ch) = cursor.next() {
-        if !ch.is_ascii_digit() {
-            if fraction_components.len() > 10 {
-                return Err(
-                    TemporalError::syntax().with_message("Fraction exceeds 9 DecimalDigits")
-                );
-            }
-
-            let fraction_value = fraction_components
-                .iter()
-                .collect::<String>()
-                .parse::<f64>()
-                .map_err(|e| TemporalError::syntax().with_message(e.to_string()))?;
-            return Ok(fraction_value);
-        }
-        fraction_components.push(ch);
+    let mut fraction_components = Vec::default();
+
+    // Assert that the first char provided is a decimal separator.
+    assert_syntax!(
+        is_decimal_separator(cursor.abrupt_next()?),
+        "fraction must begin with a valid decimal separator."
+    );
+    fraction_components.push('.');
+
+    while cursor.check_or(false, |ch| ch.is_ascii_digit()) {
+        fraction_components.push(cursor.abrupt_next()?);
     }
 
-    Err(TemporalError::abrupt_end())
+    assert_syntax!(
+        fraction_components.len() <= 10,
+        "Fraction component cannot exceed 9 digits."
+    );
+
+    let fraction_value = fraction_components
+        .iter()
+        .collect::<String>()
+        .parse::<f64>()
+        .map_err(|e| TemporalError::syntax().with_message(e.to_string()))?;
+    Ok(fraction_value)
 }
diff --git a/core/temporal/src/parser/time_zone.rs b/core/temporal/src/parser/time_zone.rs
index 810a11290aa..3b408e41501 100644
--- a/core/temporal/src/parser/time_zone.rs
+++ b/core/temporal/src/parser/time_zone.rs
@@ -11,7 +11,7 @@ use super::{
     time::{parse_fraction, parse_hour, parse_minute_second},
     Cursor,
 };
-use crate::{TemporalError, TemporalResult};
+use crate::{assert_syntax, TemporalError, TemporalResult};
 
 /// A `TimeZoneAnnotation`.
 #[derive(Debug, Clone)]
@@ -76,22 +76,20 @@ pub(crate) fn parse_ambiguous_tz_annotation(
 }
 
 fn parse_tz_annotation(cursor: &mut Cursor) -> TemporalResult<TimeZoneAnnotation> {
-    debug_assert!(is_annotation_open(cursor.peek().expect("annotation start")));
+    assert_syntax!(
+        is_annotation_open(cursor.abrupt_next()?),
+        "Invalid annotation opening character."
+    );
 
-    let potential_critical = cursor.next().ok_or_else(TemporalError::abrupt_end)?;
-    let critical = is_critical_flag(potential_critical);
-
-    if critical {
-        cursor.advance();
-    }
+    let critical = cursor.check_or(false, is_critical_flag);
+    cursor.advance_if(critical);
 
     let tz = parse_time_zone(cursor)?;
 
-    if !cursor.check_or(false, is_annotation_close) {
-        return Err(TemporalError::syntax().with_message("Invalid TimeZoneAnnotation."));
-    }
-
-    cursor.advance();
+    assert_syntax!(
+        is_annotation_close(cursor.abrupt_next()?),
+        "Invalid annotation closing character."
+    );
 
     Ok(TimeZoneAnnotation { critical, tz })
 }
@@ -122,21 +120,26 @@ pub(crate) fn parse_time_zone(cursor: &mut Cursor) -> TemporalResult<TimeZone> {
 fn parse_tz_iana_name(cursor: &mut Cursor) -> TemporalResult<TimeZone> {
     let tz_name_start = cursor.pos();
     while let Some(potential_value_char) = cursor.next() {
-        if is_tz_name_separator(potential_value_char) {
-            if !cursor.peek_n(1).map_or(false, is_tz_char) {
-                return Err(TemporalError::syntax()
-                    .with_message("Missing TimeZoneIANANameComponent after '/'"));
-            }
-            continue;
-        }
-
-        if !is_tz_char(potential_value_char) {
+        if cursor.check_or(false, is_annotation_close) {
             // Return the valid TimeZoneIANAName
             return Ok(TimeZone {
                 name: Some(cursor.slice(tz_name_start, cursor.pos())),
                 offset: None,
             });
         }
+
+        if is_tz_name_separator(potential_value_char) {
+            assert_syntax!(
+                cursor.peek_n(2).map_or(false, is_tz_char),
+                "Missing IANA name component after '/'"
+            );
+            continue;
+        }
+
+        assert_syntax!(
+            is_tz_char(potential_value_char),
+            "Invalid TimeZone IANA name character."
+        );
     }
 
     Err(TemporalError::abrupt_end())
@@ -158,14 +161,12 @@ pub(crate) fn parse_date_time_utc(cursor: &mut Cursor) -> TemporalResult<TimeZon
 
     let mut utc_to_minute = parse_utc_offset_minute_precision(cursor)?;
 
-    if cursor.check_or(false, is_time_separator) {
-        if !separated {
-            return Err(TemporalError::syntax().with_message("Unexpected TimeSeparator"));
-        }
-        cursor.advance();
+    if cursor.check_or(false, is_time_separator) && !separated {
+        return Err(TemporalError::syntax().with_message("Invalid time separator in UTC offset."));
     }
+    cursor.advance_if(cursor.check_or(false, is_time_separator));
 
-    // Return early on None or next char an AnnotationOpen.
+    // Return early on None or AnnotationOpen.
     if cursor.check_or(true, is_annotation_open) {
         return Ok(TimeZone {
             name: None,
@@ -192,22 +193,19 @@ pub(crate) fn parse_date_time_utc(cursor: &mut Cursor) -> TemporalResult<TimeZon
 
 /// Parse an `UtcOffsetMinutePrecision` node
 pub(crate) fn parse_utc_offset_minute_precision(cursor: &mut Cursor) -> TemporalResult<UTCOffset> {
-    let sign = if let Some(ch) = cursor.next() {
-        if ch == '+' {
-            1_i8
+    let sign = if cursor.check_or(false, is_sign) {
+        if cursor.expect_next() == '+' {
+            1
         } else {
-            -1_i8
+            -1
         }
     } else {
-        return Err(TemporalError::abrupt_end());
+        1
     };
     let hour = parse_hour(cursor)?;
 
     // If at the end of the utc, then return.
-    if cursor
-        .check(|ch| !(ch.is_ascii_digit() || is_time_separator(ch)))
-        .ok_or_else(TemporalError::abrupt_end)?
-    {
+    if !cursor.check_or(false, |ch| ch.is_ascii_digit() || is_time_separator(ch)) {
         return Ok(UTCOffset {
             sign,
             hour,
@@ -216,11 +214,8 @@ pub(crate) fn parse_utc_offset_minute_precision(cursor: &mut Cursor) -> Temporal
             fraction: 0.0,
         });
     }
-
     // Advance cursor beyond any TimeSeparator
-    if cursor.check_or(false, is_time_separator) {
-        cursor.advance();
-    }
+    cursor.advance_if(cursor.check_or(false, is_time_separator));
 
     let minute = parse_minute_second(cursor, false)?;