I don't think "parsed strictly" makes something hard; on the contrary, I think it's helpful to make something easy. Clear feedback, easy to test.

But then, I've always preferred strongly typed over stringly typed.

This imagines HTML as code and not markup.

The reason HTML and markdown are more widely adopted than latex is because the former are more forgiving.

I am thinking of it as markup. I stand by the point: I think "forgiving" is not a feature in parsing; it's a bug.

Forgiving is very helpful in enticing those whose content you'd like to parse to start producing content. There's no use in having the worlds greatest pipeline if nothing is being put in and moved through. See the tragedy of the death of flash and "surely someone will come along and make a great frictionless editor for canvas and webgl", only for all the creative energy ending up being sucked up and monetised by roblox, leaving the world worse off.

I see what you are saying, but I don't think catering to sloppy growth over correctness needs to happen at the document level. The unrigorous shouldn't be given access at this level, you can still make php and myspace at other layers and using other abstractions. I think sloppy growth has its place, but it also needs the right level.