'text' is not available as a prefix in functions

[DrRataplan]

repro:

https://xpath.playground.fontoxml.com/?state=H4sIAL0v4WIAA22R0UvDMBDG%2F5UjL1WYG77OWvB9gorChL1k7XUNJrmSXGbL2P%2FupXXsQaHQL8l3v%2FuSOylHDar1%2FUIddTB6bzGqtTqd1UINzoos5VftPEDJhi1WQ6%2B5W%2FZWj4dAyTfLljyTmJY1uXI1myZ%2FTM7pMFbvnYkgnwaLOnjjD8BEFloKsH3eLGD7IkjQvoHta8IwLsvVpfa3cR8nNWswzWOBjeGi%2BqQEtfaQV4BHqeUu88kDdyj9Ws6R%2Bj%2FVg3a9XPVK0HWNMYKjgHA5hTaQk9gOfQIzI5l6CObQ%2Fc%2FtMThtjf8qqidP4g%2BwT8xzHCFb5AijtIydlqWoAIyRIcUcW3J8vG2u5Enlq5erPIU8k%2BmBZCwN1jYj2uRrNrkBDrwehuHm9lR0aC3dfVOwTXF%2B2Pmdn7cKIdQyLrFeOOr8Ayss%2FhQDAgAA

Steps:

1. Declare a function with a prefix set to 'text'

Expected:

All should work. Maybe something about a prefix not being resolvable

Actual:

Parse error. Changing the prefix makes this work again

Same with element. Might be because of reserved function names.