CSS HTML Validator Standard (and higher) support spell checking in the editor and also in the validator engine. The editor supports spell checking like a typical word processing application, text editor, or HTML editor would, as well as "live spelling".

The validator engine supports spell checking by generating a single validator message with a list of words that are possibly misspelled. It can also generate a separate repeated word message.

hmtoggle_plus1Important things to know about how spell checking works
hmtoggle_plus1Downloading and installing additional dictionaries
hmtoggle_plus1Adding words to the dictionary
hmtoggle_plus1Ignoring misspelled words with "cseignorewords"
hmtoggle_plus1About the validator spelling and repeated word messages
hmtoggle_plus1Spell checker features