Re: Connecting overline and Connecting underline

From: Philippe Verdy <>
Date: Sat, 17 Nov 2012 02:33:16 +0100

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 <>

> 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
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Received on Fri Nov 16 2012 - 19:35:52 CST

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