As the first line didn't have a period, when reading this I started the parsing the second line as part of the same sentence. Not disputing whether it looks fine in the generated docs, however I won't likely ever read from the web. :-)

If only used `bool* = null` instead of an `out bool`... Perhaps `unused` is a better name than `useless` for a local var.

and needs an ending `E`. You could also say requires here, need sounds urgent. :-)

`its`

This (and maybe other places, I haven't looked too deep), could be rephrased to use a little less `we`. For instance (feel free to correct as you see fit): ``` Since semantic hasn't run yet, all that is handled here are `TypeIdentifier`, but we still need to check if it's an expression or not. ```

This comment - `TemplateParameter` or `null` - does not match the return type `bool`.

Keeping parameters on the same line is more conformant to coding style.

What column length are you keeping yourself to here? I would say 80 is standard, anything shorter just looks out of place.

I think you mean "`AliasDeclaration`s" as a plural here.

semantic passes are destructive. s/loose/lose/ ?

once semantic has run ?

Comma seems out of place here.

Write it as `asType()`, same reasons as `asFuncDecl`.

Might as well give this some ddoc love.

Maybe briefly explain this in the form of C++ mangle spec, perhaps even in the (same as passing `&function`) comment above.

`tiparent` or `parentti`?

It would be nice to have `asFuncDecl()` here so that it's clear that it has a side effect. Same goes for other places where you do this.

Using `.mangleof` testing is good, however link testing is better - though not a blocker for this.

I don't think set and reset are appropriate names here, one is `setcontext`, and the other `maybe_swapcontext`. Looking at the usage pattern of them though, `push` and `pop` seems a better fit (the Context could be chained together internally, rather than putting the brunt on the caller to keep a reference to `prev`). Not blocking however.

DMD style doesn't require space before opening parens.

As this is a ddoc comment (and others), shouldn't it be all punctuated?

Least specialized

Probably should have a comment saying why you're using visit instead of accept here.

It's a bit misleading to have a `Returns` section for a method that returns `void`.

A bit inconsistent here that none of the other branches have curly braces.

Can we please avoid abbreviations like this.