/usr/share/doc/m4/examples/patsubst.m4 is in m4 1.4.16-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 | # traceon(`patsubst')
patsubst(`GNUs not Unix', `^', `OBS: ')
patsubst(`GNUs not Unix', `\<', `OBS: ')
patsubst(`GNUs not Unix', `\<\w', `\0=')
patsubst(`GNUs not Unix', `\w*', `(\0)')
patsubst(`GNUs not Unix', `\w+', `(\0)')
patsubst(`GNUs not Unix', `\w+')
patsubst(`GNUs not '` Unix', `[ ]+', ` ')
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