@smallcircles It's basically called Korean mixed script, which is no longer used in modern Korean (both in the South and the North). Writing Korean this way is my own habit and leaves younger generations unable to read it well, so I annotated those Sino-Korean words with hangul, the Korean alphabet. Annotations are technically implemented using HTML <ruby> tags.

@hongminhee that is really cool, thank you for explaining. Marvellous Unicode and browser capabilities.

At the start of my career I developed translation software for Philips for the creation of their product manuals in N different languages, Korean among them of course. And it was before Unicode existed, so I had to manually create character mapping tables for each language's codepage and input method editor combinations. It was absolute hell doing that, ha ha. That was why this particularly caught my eye and curiosity.