Are there any references in the following {SOURCE_LANGUAGE} source code to uncommon or obscure built-in language functionality e.g. stand library calls, opcode, etc. that you do not understand and may be present in a language reference manual?

If so, return a short, comma-separated list of functions or opcodes to reference the manual for. Do not return any basic language functionality.

If not, return 'NODOCS'. 'NODOCS' must be returned on its own without further commentary.

Here is the code:
```
{SOURCE_CODE}
```
