New /prog/ challenge

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

As the first draft, I suggest to introduce:
[instruction] tags
[label] tags
[goto] tags
[variable][assign] tags
[add][subtract][mul][div][mod] tags
[int][bool][string][hex] tags
[print] tags
[if][condition][true][false] tags
[equals][not equals] tags

a BBCODE++ application:
[instruction][label]start[/label][print][mul][int]4[/int][int]27[/int][/mul][string] - one hundred and eight[/string][/print][/instruction]
[instruction][variable][name]i[/name][value][int]0[/int][/value][/variable][/instruction]
[instruction][label]increment[/label][assign][name]i[/name][value][add][name]i[/name][int]1[/int][/add][/value][/assign][/instruction]
[instruction][if][condition][equals][name]i[/name][hex]a[/hex][/equals][/condition][true][goto]end[/goto][/true][false][goto]increment[/goto][/false][/if][/instruction]
[instruction][label]end[/label][print][b][sup]your[/sup] [sub]done[/sub][/b][/print][/instruction]