silent parser errors

[bbarker]

Confusingly, parser errors do not throw.

From w3c:

Let root be a new Element, with its local name set to "parsererror" and its namespace set to "http://www.mozilla.org/newlayout/xml/parsererror.xml".

Should we build this check into the parseXMLFromString function, and throw an error if detected? Or should we make a separate function? e.g. parseXMLFromStringOrThrow

Thoughts, @toastal @garyb ?

[garyb]

It'd be nice to do something other than what the basic API provides here, yeah, as that is pretty terrible.

Does the parsererror node contain any information do you know? If so I'd suggest we change the return type to Effect (Either String Document) and take the Left information from there. If not, Effect (Maybe Document) and return Nothing on error.

[bbarker]

I like Effect (Either String Document) and am working toward that in the branch parseErrorExperiments. It seems different browsers emit the errors in slightly different ways, just to add to the fun! I'll test Firefox and a few Chromium based browsers.

One issue I came across in the above branch was purescript-web/purescript-web-dom#9, so I was in fact surfacing nulls at runtime, which should not be possible.