Regex Tester & Validator

Matches a HAML attribute expression `{...}` anchored at the start of a line (multiline flag), using a tempered dot to consume content without a single `}` while permitting doubled `}}` braces, so embedded Mustache/Handlebars `{{ }}` interpolations do not terminate the match. The trailing negative lookahead ensures the closing brace isn't part of a `}}` pair. Useful for parsing HAML templates or extracting attribute hashes in editors and linters.