-For compatibility with this program, source filenames should not
- contain Ascii whitespace or any of the following Ascii characters:
- ``!"#$%&()-:<>?\^`{|}``.
-These characters are either invalid in u·r·i’s or conflict with aspects
- of the Make or commandline syntax.
+**☡ For compatibility with this program, source file·names must not
+ contain Ascii white·space, colons (`:`), semis (`;`), pipes (`|`),
+ bucks (`$`), percents (`%`), hashes (`#`), asterisks (`*`), brackets
+ (`[` or `]`), erotemes (`?`), backslashes (`\`), or control
+ characters, must not begin with a hyphen‐minus (`-`), and must not
+ end with a cloparen (`)`).**
+The former characters have the potential to conflict with make syntax,
+ a leading hyphen‐minus is confusable for a command‐line argument, and
+ a trailing cloparen [activates a bug in G·N·U Make
+ 3.81](https://stackoverflow.com/questions/17148468/capturing-filenames-including-parentheses-with-gnu-makes-wildcard-function#comment24825307_17148894).