Specifically, I'm looking for a proxy (SOCKS or otherwise) that I can use from most browsers (Chrome on Windows, Safari on iOS) and that can accomplish the following with little configuration:
In any HTML page processed, look for HTML elements of type 'input' or 'textarea', and add the attribute 'spellcheck=false' to them.
(background: in the past few weeks, I've noticed that due to what is appearently a bug in WebKit, ALL kinds of apps, operating system dialogs, and other things have suddenly started putting red dotted underlines everywhere, even though absolutely every "Spell check" option is disabled in every configuration dialog I could find. This is hugely distracting and I don't need a spell checker. So this is a partial solution at least for surfing the web until WebKit fixes this bug).