How do the Indic scripts work in Unicode?
See Chapter 9 of the Unicode Standard, South Asian Scripts-I. Particularly relevant is the section on Devanagari, which is a detailed description not only of the Devanagari script but also outlines the model used for all similarly structured scripts in the standard. This model is the based on the ISCII model. Information about the OpenType format and the Uniscribe can be found in the excellent article Windows Glyph Processing by John Hudson.
