Re: How to add pseudo vector types

[Stefan Monnier]

> But that's sub-optimal, no?  Imagine a very large buffer which was
> narrowed to a small portion near EOB, then a modification made very
> close to EOB but partially before BEGV, then the buffer widened.  With
> your method, TS will now have to re-parse almost the entire buffer,
> whereas we know it needs to re-parse a very small portion of it.

As a general rule, we will most likely want to work hard to avoid
exposing the narrowed buffer to TS (i.e. most calls to TS will first
`widen`).

Or we will want to keep several parse trees (one per narrowing).

We have the same problem already with `syntax-ppss` which we solve by
keeping two sets of data (`syntax-ppss-wide` and `syntax-ppss-narrow`).


        Stefan