On 4/24/2020 7:44 PM, Ao Shen wrote:

Thanks for your timely reply!

Hans Hagen 于2020年4月24日周五 下午11:38写道：

...

no, but i must admit that it's kind of a border case ... i'll fix it but also wonder if *no* visual rule showing up is intended (i would then also expect an engine to show a rule .. could be an interesting new (luametatex) option as it saves kerns in some cases)

My use cases of negative vrule is a little tricky. I'm trying to comply with W3C's [Requirements for Japanese Text Layout](https://www.w3.org/TR/jlreq/). It states that

In principle, closing brackets (cl-02), commas (cl-07) or full stops (cl-06) at the line end have a half em space after them (see Fig. 3.20). This half em space can be deleted for line adjustment. However, the possibilities are only half em space or solid. Other spaces, such as a quarter em space should not be used.

The tricky part is that I also want the opening fullwidth bracket at the beginning of the line to be solid, i.e., without half em sidebearing on the left to make the left margin visually more aligned (this is one but not the only way of line begining handling shown in jlreq).

To achieve this, in the scripts handler I use the following injector between 'full_width_close' and 'full_width_open':

\hskip -0.5em \penalty 100 \hskip 0.5em minus 0.5em \vrule width -0.5em height 0pt ^^^(a) ^^^(b)

If line is broken here, the only broken points are (a) before the glue or (b) at the penalty point. With the vrule the sidebearing of the opening bracket at beginning of next line is eliminated.

In this particular case, a kern is not applicable because it won't survive the line break. And here a vrule showing nothing is intended. How about something ...

\startluacode local classes = fonts.protrusions.classes local vectors = fonts.protrusions.vectors classes.myown = { vector = 'myown', factor = 1, } vectors.myown = table.merged (vectors.quality, { [0x0028] = { 1, 0 }, -- ( [0x0029] = { 0, 1 }, -- ) }) \stopluacode \starttext \showframe \definefontfeature[whatever][default][protrusion=myown] \definedfont[Serif*whatever] \setupalign[hanging] \dorecurse{100}{(#1) } \stoptext of course you need to define the cjk fences etc. Hans ----------------------------------------------------------------- Hans Hagen | PRAGMA ADE Ridderstraat 27 | 8061 GH Hasselt | The Netherlands tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl -----------------------------------------------------------------