LAYT table proposal

This is a scratchpad for a proposed new model of OpenType layout suitable for the next major successor to OpenType.

Design principles

The font decides. Order of application of features, timing of syllabic reordering, etc. is driven by the logic within the font, not by the shaper.

field	type	notes
featurename	`TAG`	Name of this feature
n_lookups	`USHORT`	Number of lookups in this feature
start	`OFFSET`	Offset from start of table to first lookup

A lookup is a variable-length data structure which begins with the following common fields:

field	type	notes
length	`ULONG`	Length of the lookup, in bytes
opcode	`USHORT`	The opcode for this instruction. See Table of opcodes
flags	`USHORT`	Flags, as determined by the opcode

These three fields are followed by opcode-specific fields, as detailed below.