(stable) Fix some remarkup issues with selective construction of child nodes after HTML DOM parsing
The behavior of selectChildrenWithTags(...) currently isn't well-covered by tests and isn't quite right. Add coverage and fix it up.
Particularly, there's a bad call to a nonexistent method, and when we convert a tag that doesn't match the selection set into content, we incorrectly discard any paired closing tag.
Test Plan: Added failing tests, made them pass.
Reviewed By: amckinley
Differential Revision: https://secure.phabricator.com/D20630