The Editing Team want to be able to style the namespace separate from the heading in certain circumstances, as part of their talk pages project work. Example:
(see T299814)
In order to do this we need some additional markup in the h1.firstHeading, at least one additional span.
Our proposal is to just wrap the namespace name in a span for now, as this will result in no changes to main article HTML.
Note: This change is not proposing any visual change to page headings. That will be done in much more limited and scoped places such as T299814, with staged rollouts and user options.
Final markup
Pages outside of the main namespace now have the following markup in their <h1> page titles, using 'Talk:Hello' as an example:
<h1> <span class="mw-page-title-namespace">Talk</span> <span class="mw-page-title-separator">:</span> <span class="mw-page-title-main">Hello</span> </h1>
(line breaks and spaces added for readability)
Pages in the main namespace only have the last part, e.g. for 'Hello':
<h1> <span class="mw-page-title-main">Hello</span> </h1>
The new markup is not added when the title is overridden using the wikitext {{DISPLAYTITLE:…}} or -{T|…}- forms. This may be improved in the future.