-For compatibility with this program, source filenames should not
- contain Ascii whitespace or any of the following Ascii characters:
- ``!"#$%&()-:<>?\^`{|}``.
-These characters are either invalid in u·r·i’s or conflict with aspects
- of the Make or commandline syntax.
+**☡ For compatibility with this program, source filenames must not
+ contain Ascii whitespace, colons (`:`), pipes (`|`), bucks (`$`),
+ percents (`%`) or control characters, and must not begin with a
+ hyphen‐minus (`-`).**
+The former characters have the potential to conflict with make syntax,
+ and a leading hyphen‐minus is confusable for a command‐line argument.