LilyPond Contributor's Guide: 10.8.3 Write convert-ly rule

### 10.8.3 Write convert-ly rule

If the modification changes the input syntax, a convert-ly rule should be written to automatically update input files from older versions.

convert-ly rules are found in python/convertrules.py

If possible, the convert-ly rule should allow automatic updating of the file. In some cases, this will not be possible, so the rule will simply point out to the user that the feature needs manual correction.

#### Updating version numbers

If a development release occurs between you writing your patch and having it approved+pushed, you will need to update the version numbers in your tree. This can be done with:

>     scripts/auxiliar/update-patch-version old.version.number new.version.number

It will change all files in git, so use with caution and examine the resulting diff.

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