[TxMt] autocomplete in HTML - strange tags?

hello all - I was playing around with the auto-complete features in HTML (which I don't really use since I prefer snippets) and I found a whole bunch of strange tags that I don't recognize. I tried googling them but came up empty for things like "d ondblclick" and "el class" - not to mention the stranger fact that if I selected one I came up with repeating first letters - i.e. starting with <d> with insertion point inside the brackets after the 'd' gives me '<d d ondblclick="">'

so forgive my ignorance, but what exactly is this?

thanks, bennett

"the quest for knowledge is endless" -Ancient Chinese Secret