in-reply-to

 in-reply-to  is the h-entry property to use in a post that is a reply to another post. The reply post must hyperlink to the original post with.

The  property supersedes rel-in-reply-to. For more information, see rel-values.

Additionally:
 * The in-reply-to link is typically inside the reply-context of a reply post
 * The microformats2  class names can also be used to embed a reply-context with more details beyond the URL

How to consume in-reply-to
Summary: collect an ordered list of unique in-reply-to URLs by checking and adding from:
 * 1) the first h-entry for "in-reply-to" URLs (including embedded)

algorithm
Given a URL of a post, to determine the URL(s) it’s in-reply-to:


 * Let in-reply-to-urls be an empty list
 * Parse the post's HTML for microformats2. If there are any h-entries, get the first one
 * If the h-entry has an in-reply-to property, for each item in its array of values:
 * If the item is a string, append it to in-reply-to-urls if not already there
 * If the item is an embedded microformat, check if it has a url property. If it does, append the first url property value to in-reply-to-urls if not already there
 * Otherwise ignore the item
 * in-reply-to-urls is now a list of all the URLs the parsed URL is in-reply-to

You may use a different algorithm if it produces exactly the same results. E.g. you could skip checking "if not already there" conditions, and instead at the end perform a step of "* Remove duplicate values from in-reply-to-urls " - as long as you removed latter duplicates, and kept first occurrences in the list.

Usage Examples

 * tantek uses  along with   to mark-up reply notes. E.g.

Must an in-reply-to link be inside an h-entry
Q: Does an in-reply-to link have to be inside an h-entry?

A: Yes. An in-reply-to link must be inside the h-entry with class name of  so that it can be recognized as a URL property of the h-entry.

Past Research
See: For the research and development of the  property and.
 * http://microformats.org/wiki/rel-in-reply-to