title: how does a font tell the OS that "I AM a MONSPACED / FIXED-WIDTH FONT"?
body: <p>at the very first, i only want to know, why in IDE PYCHARM on Windows 10, while "show only monospaced fonts" checked, many fonts will not be listed in the editor's font selecting dialog-box[settings/editor/colors and fonts/font], also in mintty.</p>
  
  <p>I don't know how does the pycharm do, but the mintty uses the win32 API "LOGFONT".</p>
  
  <p>then, how did the windows OS know whether the font is monospaced(fixed-width)?</p>
  
  <p>i.e.:
  "source code pro" is listed, "source code pro black / extralight / light ... are not;</p>
  
  <p>"fira code" is listed, but fira code light/medium/retina are not;</p>
  
  <p>and, some other monospaced fonts are not listed there if "show only monospaced".</p>
  
  <p>it seems that pycharm only recognize the font family name when checked "show only monospced fonts"</p>
  
  <p>in OSX(Mavericks) it's a little complicated : if the 'show only monospaced fonts' was checked, pycharm could still get the family name, but it could not know which font-weight is default if the rugular weighted font version was installed.</p>
  
  <hr>
  
  <p>then, i tried to modify some fonts, and by the way having a glance to the original font's 'file-info' in font forge, but i don't know which part really effects the WINDOWS or PYCHARM(IDEA/INTELIJ/by JDK in fact?) to know which font is monospaced.</p>
  
  <p>in "OS/2" part, any parameters mentioned fixed-width/monospace/monospaced are checked, but not helped any, and in windows pycharm still can't detect them.</p>
  
  <p>so, at last, i really wonder, which parameter do TTF files or any other font file types use to tell the [windows/osx/mac os/linux] OS that 'i am monospaced'?</p>