If you want automatic built-in string validation, one option that seems particularly interesting is to use a variant of Lua patterns, which are weaker and easie

If you want automatic built-in string validation, one option that seems particularly interesting is to use a variant of Lua patterns, which are weaker and easier to understand than regular expressions, but still provide a significant degree of "sanity" for something like an email. The original version works on bytes and not runes, but you could simply write a parser that works on runes instead, and the pattern-matching code is just 400 old and battle-tested lines of C89. You might want to add one extension: allow for escape sequences to be treated as a single character (hence included in repetition operators and adding the capability to match quoted strings); with this extension, I think you could implement full email address validation: https://i.stack.imgur.com/YI6KR.png https://i.stack.imgur.com/YI6KR.png Lua patterns have also shown up in other places, such as BSD's httpd, and an implementation for Rust: https://www.gsp.com/cgi-bin/man.cgi?section=7&topic=PATTERNS https://www.gsp.com/cgi-bin/man.cgi?section=7&topic=PATTERNS https://github.com/stevedonovan/lua-patterns https://github.com/stevedonovan/lua-patterns http://lua-users.org/wiki/PatternsTutorial http://lua-users.org/wiki/PatternsTutorial