dotAll

Dotall, sometimes called single-line mode, is a regular expression option that changes how the dot metacharacter behaves. By default, the dot (.) matches any single character except newline characters. When dotall is enabled, the dot matches all characters, including newlines, allowing patterns to span multiple lines.

Many regex engines provide dotall as a distinct flag, option, or inline modifier. Common forms include the Python flag re.DOTALL (also accessible as re.S), the JavaScript RegExp flag /s, and inline patterns such as (?s) within the pattern. PCRE and other engines often support a similar inline option or the /s modifier. The dotall setting is separate from multiline mode, which affects how anchors like ^ and $ behave; multiline mode does not by itself change the meaning of the dot.

Examples:

- Python: re.compile('A.*B', re.DOTALL) matches across newlines.

- JavaScript: /A.*B/s matches across newlines.

- Inline PCRE: (?s)A.*B matches across newlines.

Usage considerations:

- Dotall is useful for parsing blocks of text where content may include line breaks, such as multiline comments or HTML-like content.

- Not all engines support inline flags identically, and some syntax may differ across languages, so portability should be tested if patterns are shared between environments.

- Enabling dotall can increase backtracking and affect performance on large inputs; use it when necessary and consider more precise patterns to mitigate worst-case behavior.