[spec] Valid whitespace characters in feature files?

[jenskutilek]

makeotf apparently allows non-breaking space characters as whitespace in feature files, while fontTools.feaLib doesn’t. Is there a list of which whitespace characters are valid somewhere?

[frankrolf]

In my opinion, all whitespace characters should be valid in feature files (even line breaks).
I have been teaching the concept that the only requirement is a semicolon to end a logical “line”.

This should be valid:

@EXAMPLE = [
    A
    B
    C
];

[khaledhosny]

Whitespace characters is a long list in Unicode (and potentially open ended with future additions to Unicode), the spec should explicitly list what characters are treated as such instead.

[frankrolf]

Since the feature file specification does not allow for non-ASCII characters, I don’t think this is an issue.

[kenlunde]

The non-breaking space is U+00A0, which is (barely) outside of ASCII, so based on @frankrolf's statement, its presence outside of comments should throw an error.

While we're on the subject, the following are the Unicode Version 10.0 characters that have the White_Space property:

0020          ; White_Space # Zs       SPACE
0085          ; White_Space # Cc       <control-0085>
00A0          ; White_Space # Zs       NO-BREAK SPACE
1680          ; White_Space # Zs       OGHAM SPACE MARK
2000..200A    ; White_Space # Zs  [11] EN QUAD..HAIR SPACE
2028          ; White_Space # Zl       LINE SEPARATOR
2029          ; White_Space # Zp       PARAGRAPH SEPARATOR
202F          ; White_Space # Zs       NARROW NO-BREAK SPACE
205F          ; White_Space # Zs       MEDIUM MATHEMATICAL SPACE
3000          ; White_Space # Zs       IDEOGRAPHIC SPACE```

[jenskutilek]

Yes, 0x0a is not ASCII, but some font editors apparently do not prevent non-ASCII characters from ending up in feature files. For example, in my case the file was in a UFO generated by glyphsLib from a Glyphs file. The feature file was UTF-8-encoded. Maybe this should be decided together with #165.