This is not a trivial subject; it requires several steps:

• decoding markup (from Markdown, simplified HTML, etc.)
• font discovery (now using fontique)
• font loading (handled by rusttype)
• font association (currently we only support a single font)
• conversion from unicode to glyphs (handled by rusttype)
• line-breaking
• shaping
• alignment
• justified alignment
• caching and rendering (glyph_brush)
• extraction of text metrics (use of line height for layouts and text highlighting)
• text position → screen position translation (drawing edit bar)
• screen position → text position translation (mouse selection/positioning)
• clipboard interaction
• glyph fallback
• rich-text clipboard support
• efficient editing for large documents: Efficient editing for larger texts kas-text#15

Currently we use glyph_brush (part of rusttype) to achieve a sub-set of the above.