They are not supposed to be zero-width. But kerning may still reduce their width contextually, as long as there's no collision.
For use in Japanese as mora indicators, given the size of glyphs used in Japanese (including Kanji characters) I don't think they should even be kerned with them, but should behave like the existing ideographic square quotation marks (and probably in this case, even their advance width would be extended to fit the alignment of ideographic squares, if they are used with an ideographic character encoded immmediately near them on their inner side, and aligned to the half-width box if their are used with an half-width character on their inner side. Fonts can contextually make these transformations of glyphs for Asian texts. Outside of these contexts, these characters should behave and be rendered like the usual [square brackets], with the same metrics and similar kerning rules. In monospaced fonts, these characters should advance by one cell and should be centered horizontally. They should also include an empty side-bearing gap between the horizontal stroke and the side of the cell (i.e. no connection/collision should be possible with characters encoded on the inner side, unless these characters are explicitly connecting outside of their own advance box, a basic macron diacritic not creating a collision because it already widdens the base character encoded with them to provide a minimum side bearing and no collision with surrounding glyphs; font authors and renderers will do their best to avoid these collisions and unexpected joinings) 2012/6/7 Stephan Stiller <[email protected]>: > Hi, > > I am excited to see the half-bracket symbols (U+2E22 -> U+2E25) in Unicode. > I've been waiting for them. I assume that they're meant for use cases such > as: > > in certain Japanese dictionaries to indicate pitch accent (U+2E22 and U+2E23 > would surround the high-register "mora") > for alternate quoting, such as Jeffrey Friedl's usage in his "Mastering > Regular Expressions" book to denote the beginning (U+2E22) and end (U+2E25) > of regexes > > In both these two use cases that I'm aware of, the symbols are zero-width, > or casually indistinguishable from zero-width. Is there a place in the > standard to indicate that this is the recommended way for fonts to implement > these symbols?
