A wiki page can be just a few paragraphs of information, or it can hold a substantial document. As with any document, when it gets longer it helps to have some organization to the information. Using Header styles helps the author organize the information. Then using an automatically maintained Table of Contents allows the reader to quickly find the desired section of the document.
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The Table of Contents ("ToC") feature works in conjunction with the paragraph styles h1 through h6. As a result, it is available in Wiki pages authored in HTML and Markdown, but not in Plain Text. This paragraph is in normal style, but the preceding one (the single word "Overview") has been marked with "h1" style. That style uses a larger default font size, and is automatically included in the ToC.
Note: there currently seems to be a quirk in the operation of the ToC button: it will not insert the ToC marker unless the page already has at least one paragraph styled as a header.
One of the weaknesses of the current ToC implementation in HTML pages is that it does not operate in a What-You-See-Is-What-You-Get ("WYSIWYG") fashion. That is, while you are in the edit mode for a page, when you use the ToC button to insert a ToC you will not see the generated ToC - instead you will see only a text marker, something that looks like this:
[TOC:Example Table of Contents:1]
When you Save the page, that marker will be converted into the filled-in and formatted ToC.
Once you've inserted the ToC marker into the page, do not use the button to update or edit the marker. Instead edit the marker itself (it is just text in the edit buffer). This is another way in which the current implementation is not WYSIWYG. A future improvement to the ToC feature may change this.
When working in Markdown pages, or as a work-around to issues with the ToC button in HTML pages, you can simply type the ToC marker. Follow the format shown above, with the keyword TOC, the Title, and the header depth separated by colons and inside of square brackets.
Table of Contents feature in wiki pages, beta@ #6948, Mark Fletcher, 2016-03-28
Basic writing and formatting syntax, GitHub-Flavored Markdown.
Link checking your wiki
There are extensions for Firefox for checking links: