“HTML Filter” processor doesn’t work as expected with regard to the set (default) HTML tags

Problem/Motivation

The “HTML Filter” processor doesn’t work as expected with regard to the set HTML tags (even with the default tags). Specifically, the tags for HTML headings (<h1>, <h2>, <h3>, …) do not work.

Proposed resolution

The cause of the problem is a bad regular expression for matching HTML tags in the input: '#^(/?)([-:_a-zA-Z]+)#'

I propose to change the regular expression to the following (see also the patch that I will attach in a minute): '#^(/?)([:_a-zA-Z][-:_a-zA-Z0-9.]*)#'

Remaining tasks

Someone with more insight into the module should review my patch. Perhaps some kind of unit test would be useful, too.

User interface changes

N/A

API changes

There are no changes to the API. Perhaps module users should update their search indexes after this change, though.