- Digits:

  - `\d+`: Matches one or more digits.
  - `\d{4}`: Matches exactly four digits.

- Non-Digits:

  - `\D+`: Matches one or more non-digits.

- Word Characters:

  - `\w+`: Matches one or more word characters (alphanumeric characters plus underscore).
  - `[a-zA-Z0-9_]+`: Equivalent to `\w+`.

- Non-Word Characters:

  - `\W+`: Matches one or more non-word characters.

- Whitespace Characters:

  - `\s+`: Matches one or more whitespace characters (space, tab, newline).
  - `\S+`: Matches one or more non-whitespace characters.

- Line Anchors:

  - `^`: Matches the start of a line.
  - `$`: Matches the end of a line.

- Character Sets:

  - `[aeiou]`: Matches any single character in the set (vowels in this case).
  - `[^aeiou]`: Matches any single character not in the set (consonants in this case).
  - `[a-z]`: Matches any single lowercase alphabetical character.

- Repetitions:

  - `*`: Matches zero or more occurrences of the preceding element.
  - `+`: Matches one or more occurrences of the preceding element.
  - `?`: Matches zero or one occurrence of the preceding element.
  - `{n}`: Matches exactly `n` occurrences of the preceding element.
  - `{n,}`: Matches `n` or more occurrences of the preceding element.
  - `{n,m}`: Matches between `n` and `m` occurrences of the preceding element.

- Alternation:

  - `|`: Matches either the pattern before or after the alternation operator.

- Grouping:

  - `( )`: Groups multiple tokens together.

- Escape Characters:

  - `\`: Escapes special characters so they can be treated as literal characters.

- Quantifiers:

  - `?`: Matches zero or one occurrences.
  - `*`: Matches zero or more occurrences.
  - `+`: Matches one or more occurrences.
  - `{n}`: Matches exactly `n` occurrences.
  - `{n,}`: Matches at least `n` occurrences.
  - `{n,m}`: Matches between `n` and `m` occurrences.

- Anchors:

  - `^`: Matches the start of a line.
  - `$`: Matches the end of a line.
  - `\b`: Matches a word boundary.
  - `\B`: Matches a non-word boundary.

- Character Classes:

  - `[abc]`: Matches any single character in the set (a, b, or c).
  - `[^abc]`: Matches any single character not in the set (any character except a, b, or c).
  - `[a-z]`: Matches any single lowercase alphabetical character.
  - `[A-Z]`: Matches any single uppercase alphabetical character.
  - `[0-9]`: Matches any single digit.

- Character Escapes:

  - `\.`: Matches a literal dot.
  - `\^`: Matches a literal caret.
  - `\$`: Matches a literal dollar sign.
  - `\(`: Matches a literal opening parenthesis.
  - `\)`: Matches a literal closing parenthesis.

- Quantifiers with Lazy Matching:

  - `*?`: Matches zero or more occurrences, but as few as possible.
  - `+?`: Matches one or more occurrences, but as few as possible.
  - `??`: Matches zero or one occurrence, but as few as possible.
  - `{n,m}?`: Matches between `n` and `m` occurrences, but as few as possible.

- Boundary Matchers:

  - `\b`: Matches a word boundary.
  - `\B`: Matches a non-word boundary.
  - `\A`: Matches the start of the input.
  - `\Z`: Matches the end of the input, before any newline characters.
  - `\z`: Matches the end of the input.

- Lookahead and Lookbehind Assertions:

  - `(?=...)`: Positive lookahead assertion.
  - `(?!...)`: Negative lookahead assertion.
  - `(?<=...)`: Positive lookbehind assertion.
  - `(?<!...)`: Negative lookbehind assertion.

- Named Groups:

  - `(?P<name>...)`: Defines a named capturing group.
  - `(?P=name)`: Matches the same text as the most recent capture group named 'name'.

- Unicode Character Properties:

  - `\p{...}`: Matches any character with the specified Unicode property.
  - `\P{...}`: Matches any character without the specified Unicode property.

- Word Boundaries:

  - `\b`: Matches a word boundary.
  - `\B`: Matches a non-word boundary.

- Matching Specific Quantities:

  - `\d{2,4}`: Matches 2 to 4 digits.
  - `\w{3,}`: Matches 3 or more word characters.
  - `\s{1,3}`: Matches 1 to 3 whitespace characters.

- Matching Specific Characters:

  - `[aeiou]{2}`: Matches any two consecutive vowels.
  - `[0-9a-fA-F]{2}`: Matches any two hexadecimal digits.

- Using Capture Groups:

  - `(\d{3})-(\d{3})-(\d{4})`: Matches and captures groups for area code, exchange code, and subscriber number in a phone number.

- Backreferences:

  - `\1`, `\2`, etc.: Matches the same text as the first, second, etc., capturing group.

- Matching Any Character:

  - `.`: Matches any single character except newline characters.
  - `[\s\S]`: Matches any character including newline characters.

- Conditional Matching:

  - `(?(condition)then|else)`: Matches 'then' if the condition is true, otherwise matches 'else'.