How do I make a deep link to a chapter or section in my Read Online version?

You can deep link right now: just set id attributes, and those are
used in place of the leanpub-auto- ones.  Then you can link to the read online version with anchor tags.
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The Markua spec has both in it:
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An auto id:
​https://leanpub.com/markua/read#leanpub-auto-todo-in-leanpub
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A manually set id:
​https://leanpub.com/markua/read#resource-types-and-formats
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