`: root-relative path name of file being printed
    :``%H``: changeset hash (40 hexadecimal digits)
    :``%R``: changeset revision number
    :``%h``: short-form changeset hash (12 hexadecimal digits)
    :``%r``: zero-padded changeset revision number
    :``%b``: basename of the exporting repository
    :``\``: literal "\" character