Raising custom exceptions and tracking them in proc signatures

[adnan]

Hi, as far as I know Nim has exception tracking:
    
    
    proc doRaise() {.raises: [IOError].} =
      raise newException(IOError, "IO")
    
    
    Run

1\. Where are the common error types like "IOError" defined in the stdlib?

2\. I want to throw a custom exception. How can I annotate them?
    
    
    proc dosSomething() =
      if someCondition: raise newException(<A proper Error>, "Adverse condition 
found")
      # ...
    
    
    Run