A bit of helping hand on how to work with existing PRs.
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+
+# What to do with existing GitHub PRs?
+
+A pull request is a bunch of commits forking for some other
+commit. As such, the same commits should be applicable to the
+forked repository (Solr or Lucene), at least initially (until
+the folder structure changes, for example).
+
+Here is a sample workflow to apply an existing pull request from
+Lucene:
+
+https://github.com/apache/lucene-solr/pull/2459
+
+1. You can just apply this PR directly as a patch:
+
+git clone https://github.com/apache/lucene.git
+cd lucene
+wget https://github.com/apache/lucene-solr/pull/2459.patch
+git apply 2459.patch
+git add -A .
+git commit -m "Applying PR # ..."
+git push
+
+2. You can "rebase" the PR via a separate fork on github. This preserves commit
+ history but is slightly longer. Example:
+
+- create a github fork of the lucene repository (mine at https://github.com/dweiss/lucene)
+- locate the source repository and branch of the PR. For our example:
+ https://github.com/apache/lucene-solr/pull/2459
+ the source is:
+ https://github.com/donnerpeter/lucene-solr/tree/revTrie
+
+- Now create a "cloned" PR:
+# clone your own fork
+git clone https://github.com/dweiss/lucene.git
+cd lucene
+# add pr's repository as the remote and fetch commits from there
+git remote add donnerpeter https://github.com/donnerpeter/lucene-solr.git
+git fetch donnerpeter
+# get the PR's branch:
+git checkout donnerpeter/revTrie -b revTrie
+# push to your own fork
+git push origin HEAD -u
+# The above will display a PR-creating link but you can also do this manually:
+https://github.com/apache/lucene/compare/main...dweiss:revTrie
+Look at the PR and create it if it looks good.
+# This example's PR was at:
+https://github.com/apache/lucene/pull/2
