* Allow CSS selectors with whitespace in `hx-trigger`
Parsing of `hx-trigger` scans for whitespace, so if a CSS selector is used that contains whitespace, e.g. `form input`, a syntax error is raised.
A workaround is implemented by allowing such a CSS selector to be wrapped in either curly braces or parentheses.
* Add explanation whitespace in CSS selector to docs
* Tests for CSS selectors containing whitespace
* Use faster RegEx test, remove redundant variable declarations
* Added Descendant Combinator support to `root` and `target` modifiers
* Add missing semicolon
* Tests for descendant combinators in `root` and `target` modifiers
* Improve descendant combinator test coverage
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