docs: def warn_explicit(message, category, filename, lineno,
                        module=None, registry=None, module_globals=None,
                        emit_module=None):
      """
      Low level implementation of the warning functionality.
      Duplicate of the standard library `warnings.warn_explicit`,
      except it accepts the following arguments:
  
      `emit_module`: regular expression that should match the module the warnings
                     are emitted from.
  
  
      """
      lineno = int(lineno)
      if module is None:
          module = filename or "<unknown>"
          if module[-3:].lower() == ".py":
              module = module[:-3]  # XXX What about leading pathname?
      if registry is None:
          registry = {}
      if registry.get('version', 0) != warnings._filters_version:
          registry.clear()
          registry['version'] = warnings._filters_version
      if isinstance(message, Warning):
          text = str(message)
          category = message.__class__
      else:
          text = message
          message = category(message)
      key = (text, category, lineno)
      # Quick test for common case
      if registry.get(key):
          return
      # Search the filters
      for item in warnings.filters:
          item = _get_proxy_filter(item)
          if len(item) == 5:
              action, msg, cat, mod, ln = item
              emod = None
          else:
              action, msg, cat, mod, ln, emod = item
          if ((msg is None or msg.match(text)) and
             issubclass(category, cat) and
             (mod is None or mod.match(module)) and
             (emod is None or emod.match(emit_module)) and
             (ln == 0 or lineno == ln)):
              break
      else:
          action = defaultaction
      # Early exit actions
      if action == "ignore":
          registry[key] = 1
          return
  
      # Prime the linecache for formatting, in case the
      # "file" is actually in a zipfile or something.
      import linecache
      linecache.getlines(filename, module_globals)
  
      if action == "error":
          raise message
      # Other actions
      if action == "once":
          registry[key] = 1
          oncekey = (text, category)
          if onceregistry.get(oncekey):
              return
          onceregistry[oncekey] = 1
      elif action == "always":
          pass
      elif action == "module":
          registry[key] = 1
          altkey = (text, category, 0)
          if registry.get(altkey):
              return
          registry[altkey] = 1
      elif action == "default":
          registry[key] = 1
      else:
          # Unrecognized actions are errors
          raise RuntimeError(
              "Unrecognized action (%r) in warnings.filters:\n %s" %
              (action, item))
      if not callable(warnings.showwarning):
          raise TypeError("warnings.showwarning() must be set to a "
                          "function or method")
      # Print message and context
      warnings.showwarning(message, category, filename, lineno)