-For compatibility with this program, source filenames should conform to
- the following rules :—
-
-- They should not start with a hyphen‐minus.
- This is to prevent confusion between filenames and options on the
- commandline.
-
-- They should not contain spaces, colons, percent signs, backticks,
- question marks, hashes, or backslashes.
-
-In general, filenames should be such that they do not require
- percent‐encoding in the path component of an i·r·i.
+**☡ 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.