ICU: What does NFD and NFC mean?

Question

I found a snippet which reads

Any-Latin; NFD; [:Nonspacing Mark:] Remove; NFC; [:Punctuation:] Remove; Lower();

...and is supposed to make arbitrary string well fitting into a URL.

So, I guess the things between the semicolons are something like "commands" which are to be executed, but what particularly does NDF and NFC stand for? I really did find nothing even in the official documentation...

Answer 1

See ICU transliterators and the linked page on TR15 normalization forms for complete examples.

Normalization Form D (NFD) Canonical Decomposition

Normalization Form C (NFC) Canonical Decomposition, followed by Canonical Composition

Normalization Form KD (NFKD) Compatibility Decomposition

Normalization Form KC (NFKC) Compatibility Decomposition, followed by Canonical Composition