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Error handling

Compile-time errors

1. Directive errors:
   1. unknown directive
   2. Multiple directive definitions
   3. more than one directive per line
   4. syntax, esp. with #hide, #show, #showif, #query
   5. non-existent file with #load, #include
   6. #bool recognised but not supported
   7. #nc discontinued
   8. #seed ... etc.
2. Missing node
3. Missing colon
4. Missing opening or closing LHS <, >
5. Non-atom in LHS path
6. Missing equality token
7. Missing opening or closing "
8. Missing opening or closing RHS <, >
9. Non-atom in RHS path
10. Missing final point (cf. last node - not handled)
11. Multiple directive definitions

Runtime errors

1. Low memory
2. Buffer overflow
   1. very long paths
   2. very long value sequences
   3. very long equations
   4. very long nodes
   5. deep or infinite recursion
   6. very large input files
3. Connect errors: reporting about the exact place where an undefined value encountered:
   1. Undefined node
   2. Undefined path
4. Correct extensions (a notorious problem in early implementations)