Visible Glyphs for Non-visible Characters

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ClintGoss
Posts: 69
Joined: Mon Nov 06, 2017 2:18 pm

Visible Glyphs for Non-visible Characters

Post by ClintGoss » Thu Feb 13, 2020 2:58 pm

Should I use visible glyphs for code points that normally render invisibly?

For U+FEFF ZERO WIDTH NO-BREAK SPACE, my fonts had a glyph with no contours and zero advance width.

Then I saw the SIL document Recommended Characters for Non-Roman Fonts (https://scriptsource.org/entry/gg5wm9hhd3), which suggests:
"BYTE ORDER MARK, making this visible might be helpful". Now this character is somewhat deprecated (I think there's a preferable WORD JOINER character), and I think the recommendation is based on visualizing a bytestream with the ubiquitous BOM character.

So I've started using this character in my fonts for U+FEFF, combining the BOM indicator with the Unicode intent of ZWNBS:
BOMdesign_200.png
BOMdesign_200.png (23.24 KiB) Viewed 54 times
... but ... Could this cause heartburn for users?

MS Word (Office 365, Win10x64) seems to compose its own character, regardless of the font in use. With ...

File => Options => Display => Show All Formatting Marks or
File => Options => Display => Optional Breaks

... turned on, U+FEFF shows up as:
WordTestFEFF_master.png
WordTestFEFF_master.png (15.22 KiB) Viewed 54 times
... so the glyph that Word uses does appear to be composed on-the-fly based on some font metric, and does not relate to what is in the font.

I surveyed every installed font I have, and no font has a visible glyph at U+FEFF. They are all either blank or default to .notdef.

In addition to U+FEFF, the SIL Recommendations document lists other code points that should get visible glyphs. For example, there is a long (and impenetrably dense, to me) rationalization for why visible glyphs might be helpful for the Variation Selector characters (they name the 16 in the BMP, but omit the ones up beyond the BMP).

Should I install glyphs like this in the U+FE00-U+FE0F range??
VS1Design_200.png
VS1Design_200.png (21.44 KiB) Viewed 54 times

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