MediaWiki's core jquery.placeholder module and https://github.com/mathiasbynens/jquery-placeholder should be merged. Both are polyfills for 'placeholder' attribute implementation, with each having some features missing from the other one.

The final result should pass unit tests of both modules (they are both using QUnit for testing, so they should be easy to migrate); see Manual: JavaScript unit testing on MediaWiki.org. mathiasbynens/jquery-placeholder's tests should be incorporated into MediaWiki's jquery.placeholder ones.

See this bug report for more information. Students are required to read Wikimedia's general instructions first. You are only required to submit a patch to MediaWiki. (But feel free to submit a pull request on GitHub too.)