The 12/12/17 deployment was derailed by a huge number of unsupported_sections errors thrown by throwIfPreviousSectionIsIncomplete (link). This is a function to check that all sections have titles and anchors. However, the assumption that every section should have a title and anchor doesn't seem to be valid for the project main page or for non-content namespaces. We should figure out how to handle these situations gracefully.
Do nothing for Parsoid sections with IDs of -1 and -2; log warnings rather than throwing errors for sections with IDs >= 0 that fail the check for presence of heading and anchor. (See T182774#3834556 and T182774#3834568 for discussion.)