code: func (g *Graph) DebugOperation(operation string, info string) DebugOperationEnd {
  	return g.debug.BeginOperation(operation, info)
  }
docs: // DebugOperation marks the start of a set of graph transformations in
  // the debug log, and returns a DebugOperationEnd func, which marks the end of
  // the operation in the log. Additional information can be added to the log via
  // the info parameter.
  //
  // The returned func's End method allows this method to be called from a single
  // defer statement:
  //     defer g.DebugOperationBegin("OpName", "operating").End("")
  //
  // The returned function must be called to properly close the logical operation
  // in the logs.