diff --git a/parser/src/scanner.rs b/parser/src/scanner.rs
index ae77813..4da5515 100644
--- a/parser/src/scanner.rs
+++ b/parser/src/scanner.rs
@@ -211,38 +211,55 @@ impl<T: Iterator<Item = char>> Iterator for Scanner<T> {
     }
 }
 
+/// Check whether the character is nil (`\0`).
 #[inline]
 fn is_z(c: char) -> bool {
     c == '\0'
 }
+
+/// Check whether the character is a line break (`\r` or `\n`).
 #[inline]
 fn is_break(c: char) -> bool {
     c == '\n' || c == '\r'
 }
+
+/// Check whether the character is nil or a line break (`\0`, `\r`, `\n`).
 #[inline]
 fn is_breakz(c: char) -> bool {
     is_break(c) || is_z(c)
 }
+
+/// Check whether the character is a whitespace (` ` or `\t`).
 #[inline]
 fn is_blank(c: char) -> bool {
     c == ' ' || c == '\t'
 }
+
+/// Check whether the character is nil or a whitespace (`\0`, ` `, `\t`).
 #[inline]
 fn is_blankz(c: char) -> bool {
     is_blank(c) || is_breakz(c)
 }
+
+/// Check whether the character is an ascii digit.
 #[inline]
 fn is_digit(c: char) -> bool {
     c.is_ascii_digit()
 }
+
+/// Check whether the character is a digit, letter, `_` or `-`.
 #[inline]
 fn is_alpha(c: char) -> bool {
     matches!(c, '0'..='9' | 'a'..='z' | 'A'..='Z' | '_' | '-')
 }
+
+/// Check whether the character is a hexadecimal character (case insensitive).
 #[inline]
 fn is_hex(c: char) -> bool {
     c.is_ascii_digit() || ('a'..='f').contains(&c) || ('A'..='F').contains(&c)
 }
+
+/// Convert the hexadecimal digit to an integer.
 #[inline]
 fn as_hex(c: char) -> u32 {
     match c {
@@ -252,6 +269,8 @@ fn as_hex(c: char) -> u32 {
         _ => unreachable!(),
     }
 }
+
+/// Check whether the character is a YAML flow character (one of `,[]{}`).
 #[inline]
 fn is_flow(c: char) -> bool {
     matches!(c, ',' | '[' | ']' | '{' | '}')