I'm not sure that the combining low lines and overlines should connect by moving them up or down depending on the surrounding grapheme clusters that they DON'T modify directly.
If you want a true connection, this is a text decoration around the *full* text span (includong multiple clusters), and so it does not work as a combining character. And even in the case of traditional underlining styles, they do not necessarily connect (for example the underlining is often stopped around descenders, instead of crossing them, or instead of moving down the underlining stroke, something that is performed using a border relative to the bounding box of the span). But the combining overline or low line should probably not be interrupted across descenders/ascenders (except in specific font style designs that use various swashes and decorations) They should however be at least as long as the advance width to cover it completely (unlike upper and lower macrons that should not connect at all and should probably never intersect or touche the ascenders and descenders : this is the main difference of these macrons), except if the base character is surrounded in its style by a border decoration (e.g. in a "keycaps" font style), in which case, these low lines and overlines should be as long as possible to remain within this border decoration, and probably not touching it, the base character and all is combining marks being completely rendered in the middle of this decoration. Some font styles will not permit any connection as there's a mandatory gap between cluster cells for this style. In addition, some other text effects may not change the length of these low lines and overlines, such as when there's a intercharacter justification. On the opposite, the connection is mandatory for some scripts like Arabic or some Indic scripts, where characters should be joined according to their joining properties (the renderer automatically inserts these connections for text justification if needed) without even having to use any combining characters: these connections are part of the intercharacter "blank" gaps. 2012/11/16 Andreas Prilop <[email protected]> > U+0305 Combining overline > U+0332 Combining low line > should both "connect on left and right". > > Which software (program and font) actually does this > when you overline/underline "gh"? > Test at > http://www.user.uni-hannover.de/nhtcapri/combining-marks.html > > -- > Outgoing mail is certified free from defamation of Islam™ > and insult of the Prophet™. > Checked by Thinkpol anti-obscenity system v. 6.66. > >
