Finding catcode of a character in a cctab from outside

[blefloch]

While implementing #877 about catcodes produced by l3regex I thought of a nice extension, which would be to use some particular catcode table. The easiest/fastest approach for this would be to have a way to access particular entries in a catcode table without actually running \cctab_begin:N.

The key question is whether this is accessible from the Lua side in LuaTeX (alternatively I guess one could switch to the given catcodetable locally, and look up the catcode on the TeX side). A possible implementation for non-luatex engines is

\int_compare:nNnTF {#2} < { 256 }
  { \intarray_item:Nn #1 { #2 + 1 } }
  { \char_value_catcode:n {#2} }

[zauguin]

The key question is whether this is accessible from the Lua side in LuaTeX

It is. (tex.getcatcode (42, 0x4242) gives the catcode of char U+4242 in table 42)