code: func (c *Configs) setConfig(confName configName, value *ConfigSettings) {
  	assert(len(confName) == len(c.ConfigVariables))
  	assert(value != nil)
  	key := confName.key()
  	pair, ok := c.byConfig[key]
  	assert(!ok, "setConfig must not override existing keys (%s => %v)", key, pair.value)
  	c.byConfig[key] = configPair{confName, value}
  }
docs: // setConfig sets the ConfigSettings for this key.
  //
  // The key is a tuple of bounded or unbounded variables. The global variable
  // is the key where all values are unbounded.