User:SPage (WMF)/Sandbox
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If you take these two paragraphs, each with a translation element <!--T:NN-->:
For an introductory guide to developing MediaWiki,
For help installing or customizing MediaWiki, ...
and turn the items into bullets and remove the blank line between them because whitespace between bullets is significant and puts them in separate <code><ul></code> elements, bam you get errors because the two translation elements must have whitespace between them. You get
Multiple translation unit markers for one translation unit.
Translation unit text:
<!--T:2--> * For an introductory guide to developing MediaWiki, <!--T:3--> * For help installing or customizing MediaWiki, ...
This is not explained at all in translation documentation. It's only mentioned in passing on pages like Help:Extension:Translate/Page translation administration.