A full data: URL, e.g. data:image/png;base64,iVBOR….
The MIME type (image/png), or null when the URL is malformed.
Stops at the first ; or ,, so encoding parameters stay out of the result.
Exported as the single parser for this format: a hand-rolled variant in
utils/validators/general-validators.ts used to return image/png;base64
— harmless against a startsWith("image/") test, but wrong against an exact
whitelist. Sharing the parser is what makes sharing the whitelist safe.
Extract the MIME type from a
data:URL.