HtmlParameterExtractor

Pulls a modifier parameter out of a matched HTML element. Receives the element name and the raw attribute slice between it and the closing > (e.g. span and style="color:red" for <span style="color:red">). Returns the parameter to splice into the UniText source tag (Empty for a parameterless match), or null when the element does not actually carry this modifier (a <span> without the expected CSS property, or a semantic element whose inline style cancels it).