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.