Just published: First Public Working Draft of Khmer Layout Requirements.
https://www.w3.org/TR/khmr-lreq/

The document points to sources of requirements, discussions relevant to Khmer, tests, etc. In time, more descriptive text may be added to the document itself.

This document supports the Khmer Gap Analysis document.
https://www.w3.org/TR/khmr-gap/