Doxygen ignores txt files. Following is set in cfg:
FILE_PATTERNS = *.bash \
*.c \
*.txt \
EXTENSION_MAPPING = lua=C \
sed=C \
sh=C \
bash=C \
txt=C
FILTER_PATTERNS = *.lua=lua2dox \
*.sed=doxygen-bash \
*.sh=doxygen-bash \
*.bash=doxygen-bash \
*.txt=doxygen-bash
The filters work. Same file with sh or bash extension gets parsed properly.