[XeTeX] Typographical question: xetex' default wordspacing (\fontdimen2--7)

Toralf Senger Senger at mpimp-golm.mpg.de
Sun Jun 25 07:11:47 CEST 2006

>Jonathan Kew <jonathan_kew at sil.org> writes:
>> So in both cmr10 and cmr12, the extra-space value seems to be the  
>> same as the shrink value, at 1/3 of the space width (not 1/6, as  
>> suggested above).

>That's also what can be found in the TFM files, eg:

Yes, that was a typo- 1/3 is what I found in Computer modern fonts. OTFtoTFm calculates extra-space as 1/6 of space and the webpages that describe fontdimens 1--7 do recommend that.

>I know that current PSNFSS uses fontinst for creating the metrics which uses
>ie, STRETCH = 600/1000 SPACE and SHRINK = EXTRASPACE = 240/1000 SPACE
>| \comment{The remaining code in this section sets various metric 
>| parameters for the font. Ideally, all these parameters should already  
>| have been set; the values computed here are merely crude guesses 
>| about what might be the right value.}

Interesting! So who sets those parameters IDEALLY? And based on what reasoning?

>>At least, fontdimen 7 (extra space) should be made the same 
>>as fontdimen 4 (shrink); 1/3*space is probably a reasonable value for this.


>> How about fontdimen 3  
>> (stretch).... should we reduce this from 2/3 to 1/2? This would tend  
>> to give more consistent spacing, but would also increase the  
>> likelihood of xetex reporting overfull/underfull boxes where it is  
>> unable to achieve a good enough paragraph layout.

That may be true. But I think fontdimens are not the right place to worry too much about the paragraph-setting capabilities of TeX. There are amble of other parameters which controll that:
\penalty, \linepenalty, \hyphenpenalty, \exhyphenpenalty,
\adjdemerits, \doublehyphendemerits, \finalhyphendemerits,
\pretolerance, \tolerance, \emergencystretch,\looseness

So I think one could TeX at least give the chance to typeset a document beautifully, which implies to be rather strict with the 'strech' paramter. I used 'strech=1/2*space' for most fonts (due to OTFtoTFM default setting), I write many texts in german, but I see rarely a overfull \hbox. Usually the problem can be solved by giving Tex some hyphenatin advice or rephrase. If one does not want to do that and a paragraph is really bad with lines sticking into the margings, on could put a \sloppy in front of that (which to make TeX relax a bit (and make spacing worse)...

>1/2 is definitely appropriate for most English texts.

For German as well. Therefore I agree with a 'stretch'=1/2*space, 'shrink'=1/3*space, 'extra space'=1/3*space. However (directed to Jonathan), I would give the opinion of people more weight, who have more typographical knowledge than me..

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