New /prog/ challenge

Write a touring-complete BBCODE++ interpreter as a Greasemonkey extension.

Instead of making BBCode Touring complete, we should have a markup language based on s-expressions, something like

(b We are (i about to study the idea of a computational process.) Computational processes are abstract beings that inhabit computers.) (m As they evolve, (b processes) manipulate other abstract things called data.) The evolution of a process is directed by a pattern of rules called a program. People create programs to direct processes. In effect, (sup we (sub (b conjure the spirits)) of the computer) (spoiler with our spells.)

Which would be parsed as

We are about to study the idea of a computational process. Computational processes are abstract beings that inhabit computers. As they evolve, processes manipulate other abstract things called data. The evolution of a process is directed by a pattern of rules called a program. People create programs to direct processes. In effect, ^{we _{conjure the spirits} of the computer} with our spells.