In #2761 I introduced a new API, struct Mailbox *ctx_mailbox(struct Context* ctx), which has the sole purpose to avoid boilerplate like if (Context && Context->mailbox).

I would like to use the API more extensively, whenever Context->mailbox is used. This needs to be done with care as Context is a global variable and its contents might change when calling other functions.

This would

Currently there are several matching functions not implemented, ex: doc, xls, flac, [wav](https://github.com/gabriel-vasile/mimetype/blob/master/matcher

What I did: json.Marshal(envelope)

What I expected: convert an Envelope object into Json

What I got: a stack overflow when envelope contains at least one part

Release or branch I am using: master

Please find attached a file to reproduce. As I understand the problem, there is an infinite loop while walking the Envelope object as we can go to Envelope.Root.FirstChild.Parent.FirstChild.Pa

In https://mimesniff.spec.whatwg.org/#parsing-a-mime-type the following step might be clearer if it explicitly said the trailing sequence after " was to be discarded. Might also be better if the example contains a ';' since the step mentions ';'

Current:

Collect a sequence of code points that are not U+003B (;) from input, given position.
Example: Given text/html;charset="shift_jis"iso-20