An upstream changelog file may be specified as an option. If none is specified, dh_installchangelogs may look for files with names that seem likely to be changelogs as described in the next paragraphs (assuming the package is using compatibility level 7 or above).
In non-native packages, dh_installchangelogs will first look for changelog files installed by the upstream build system into usr/share/doc/package (of the package build directory) and rename the most likely candidate (if any) to usr/share/doc/package/changelog. Note that dh_installchangelogs does not look into any source directory (such as debian/tmp). Otherwise, dh_installchangelogs (at compatibility level 7 or any later) will look for changelog files in the source directory (e.g. the root or the docs subdirectory).
If there is an upstream changelog file, it will be installed as usr/share/doc/package/changelog in the package build directory.
If the specified upstream changelog is an html file (determined by file extension), it will be installed as usr/share/doc/package/changelog.html instead. If the html changelog is converted to plain text, that variant can be specified as a second upstream changelog file. When no plain text variant is specified, a short usr/share/doc/package/changelog is generated, pointing readers at the html changelog file.
Use the package specific name if package needs a different NEWS or changelog file.
The changelog file is installed with a name of changelog for native packages, and changelog.Debian for non-native packages. The NEWS file is always installed with a name of NEWS.Debian.
Note that directory name of the changelog is also part of the match.