It's not hard to grab expressions in brackets, as long as there's only one level -- as long as brackets never appear inside other brackets, or escaped or as part of quoted text.

If, on the other hand, your expressions can ever look like

[w([one]|[two]|[three]|[four])]
[download]

or maybe

[w(one bracket \)|two brackets \))]
[download]

or

[w(one of these ")"|one of these "]")]
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then we're in a whole other territory.

---

($_='kkvvttuubbooppuuiiffssqqffssmmiibbddllffss')
 =~y~b-v~a-z~s;                             print
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