Support `startsWith` selector

Want to index edgedb docs https://www.edgedb.com/docs/datamodel/index

Docs exist inside this class `layout_docsContent__JzhPH` where `JzhPH` changes page to page.

Currently the selector wants fixed value. Would be nice to support `[class^="layout_docsContent__JzhPH"]` essentially.

No file or test is named in the issue. Start by locating the TypeScript code that validates or applies CSS selectors, then check how fixed class selectors are handled for the EdgeDB documentation URL. Done means selectors using a class prefix such as [class^="layout_docsContent__JzhPH"] are accepted and the existing fixed-value behavior still works.

Written by the indexing model from the issue text.