Re: [csswg-drafts] [css-fonts] Handling of Standardized Variation Sequences

I find the second part of this statement

> The fallback to `b` behavior is problematic because it may not be what the author intended and the user has completely no idea. More often, the preferred behavior is that a "tofu" (.nodef) is displayed instead.

somewhat surprising. Displaying a .notdef glyph makes the intended character completely opaque to the reader; there is no clue as to what the author intended. It's hard to imagine a situation where this would be desirable for a reader.

ISTM that a more useful fallback, in the case where no available font supports the sequence `b + c1`, might be to render `b,  .notdef`, or even `b, <visual representation of VS code>`; i.e. the reader would see the base glyph, and therefore be able to read the character, but would also see some kind of additional mark -- even if only a tofu -- which provides a clue that there is "something special" about the text at this point.

This would, however, conflict with Unicode's classification of the variation selectors as Default Ignorable codepoints, which implies that when not supported, they should have no visible rendering: "When such a special-use character is not supported by an implementation, it should not be displayed with a visible fallback glyph, but instead simply not be rendered at all." (Unicode, ยง5.3.)

This suggests that fallback to `b` (with no visible indication of the unsupported variation selector) is the correct default behavior when no available font supports `b + c1`; a mode that makes the variation selector visible would be a special, non-default rendering comparable to a word processor's "show invisibles" mode that adds visible marks to spaces, tabs, carriage return, etc.


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Received on Thursday, 8 March 2018 09:47:55 UTC