Collapsible section headings get generated in different ways based on whether Parsoid or the legacy parser is in use.

To keep our lives simple, we'd love to focus on just the Parsoid output. But EnWiki (where we will be prototyping, alongside some other wikis) still uses the legacy parser.

Is there an easy way to programmatically "opt in" visitors to Parsoid even if they would not otherwise get it – ideally in say a MW hook like onBeforePageDisplay?

Acceptance Criteria

• Determine whether we need to limit our experiment to just Parsoid (markup is different vs legacy parser)
• If this is necessary, determine how to best achieve this (actual implementation can be handled in a follow-up task)

Decision

We will focus on the legacy parser for the A/B test since that's what the target wikis are using.

More information here: https://docs.google.com/document/d/1mir0XNxhhBx6cPNP9Jt43wZg_D8kU_6YbEOQH8G0mAM/edit?tab=t.0.