Under copyright (with permission)
You need to know why a plant name is ”naked” (nomen nudum), why the ”combination is invalid”, why a name has ”priority”? Then, read the electronic version of the code at International Code of Botanical Nomenclature (Vienna code, 2006). Sorry, the english version cannot be downloaded.
Conversely, you may download an official french translation: CodeNomenFr.pdf (0,4Mo; 2008-12-05). You must comply with the rules (in french!) defined by tela-botanica to use this file. 1)
The last issue of the code (2006, Vienna) can be read here