(i'm not sure if this question must be here or not, feel free to move it if it should be somewhere else)

my main goal is described here. the question i have is how can Microsoft Word or Wordpad or other word editing software render fonts when these fonts seems to not follow the same rules? and how do they render characters glyph based on adjacent(or sometimes even further neighboring) characters?

for example look at this font(it is free). opening it using font forge i learned that codepoints from U+FE00 to U+FE87 are assigned to glyphs that do not represent those code points characters. still when you type in Word using that font and entering the keystrokes for those glyphs, the glyphs are rendered correctly. note that these glyph represent characters that do not have specific keys on keyboard, but are different forms of other characters. for example " ﻟ " is initial form of " ل " so Word must have some instruction(built-in instructions or instructions stored in font file) to render the desired form instead of isolated form.

another example is the font IranNastaliq(also free) which is a very popular font in farsi and it's output is like calligraphy done in farsi. so it has lots of glyphs for combination of characters, etc.

so how does Word render these? how can i mimic it? how can i read the instructions(if there is any) inside of the font file?