Research the dieresis situation

There’s strange contradiction I even had to describe in the documentation:

How to know that O 177 is the same as code="196"? To do that, first look into cmmi10.vpl file: there’s the following entry:

(CHARACTER O 177 (comment dieresis)
   (CHARWD R 583)
   (CHARHT R 705)
   (CHARIC R 118)
   (MAP
      (SETCHAR O 151)
      )
   )

That means that O 177 is named dieresis. Then, open Adobe Glyph List and search for the dieresis name:

dieresis;00A8

It means that O 177 should be character 0xa8 or 168, not 196. The reason for that contradiction is currently unknown.

We need to research that: what does code="196" mean and what’s the reason the diaresis isn’t 168?

We need to find the answer and write in into the documentation.

[prepare]

That is my first report…

I also need to investigate more.

[prepare]

I think your XML was created from some complex ‘Tex’ tool.

---

At this time…

… That means that O 177 is named dieresis

Why dieresis is marked as O 177

We need to go to the original glyph definition of the cm font (https://ctan.org/tex-archive/fonts/cm/mf)

I think dieresis is here => http://mirror.hmc.edu/ctan/fonts/cm/mf/accent.mf (scroll to the end of the page)

cmchar “Umlaut (double dot) accent”; numeric dot_diam#,dot_diam; dot_diam#=max(dot_size#,cap_curve#); beginchar(oct"177",9u#,min(asc_height#,10/7x_height#+.5dot_diam#),0); dot_diam=max(tiny.breadth,hround(max(dot_size,cap_curve)-2stem_corr)); italcorr h#*slant+.5dot_diam#-2.25u#; adjust_fit(0,0); pickup tiny.nib; pos1(dot_diam,0); pos2(dot_diam,90); x1=x2=2.75u; top y2r=h+1; if bot y2l<x_height+o+slab: y2l:=min(y2r-eps,x_height+o+slab+.5tiny); fi y1=.5[y2l,y2r]; dot(1,2); % left dot pos3(dot_diam,0); penpos4(y2r-y2l,90); y3=y4=y1; x3=x4=w-x1; dot(3,4); % right dot penlabels(1,2,3,4); endchar;

beginchar(oct"177",

At that time, it may be called ‘Umlaut accent’ or ‘double dot’ accent.

and then some tool map it to the name “dieresis” later.