Background
GrowthExperiments (tries to) manipulate with the default behaviour of the CAPTCHA extension. Specifically, ConfirmEmailHooks::onAuthChangeFormField attempts to adds a "what is this?" link, see the message as an example.
Problem
There are two problems with this hack. Most importantly, changing the label is a highly unusual integration with ConfirmEdit (the extension powering CAPTCHA). Non-standard integrations are error-prone, which brings me to the second problem...
...During several tries, I was actually unable to reproduce this behaviour. The CAPTCHA field in create account looks always the same, regardless of whether GrowthExperiments is enabled. Below, you can find screenshots from enwiki and enwikivoyage (those two projects were picked, as enwiki has GrowthExperiments, and enwikivoyage doesn't).
| enwiki screenshot | enwikivoyage screenshot |
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I'm also unable to trigger the link on other Growth projects.
Solution
Given the link broke and no one complained (likely for months, if not years), I propose to remove the code powering this capability. If we do not want to remove it, I suggest to move it to ConfirmEdit itself (upstreaming it), where it can be done in a sustainable way.