Extension:GettingStarted/Architecture discussion

HTML and CSS relationship
But the HTML uses MediaWiki:gettingstarted-msg, and the default value of that is 'An administrator on should customize this message by editing    :gettingstarted-msg.'.

Basically, the CSS is implicitly depending on HTML outside of the extension, with the default message being a placeholder. This leads to inconsistencies if we're not careful.

With Munaf's latest styling (Gerrit in progress), it should be possible to have default chrome HTML (everything outside the three columns), with a transclusion to another page. In English Wikipedia's case, that include would be the Copyediting/Spelling & grammar/Add links columns, populated by SuggestBot initially.

Does it make sense to put that outer HTML with an include as the default message?
 * CSS that's specific to the inner wiki-specific part, should probably go in a CSS page in the MediaWiki namespace. This can use essentially the same mechanism as GuidedTour uses for wiki-specific CSS.