Read the section "Subtree Merges and Subtree Mergeinfo" under Basic Merging. It is basically removing the redundant subtree mergeinfo as the needed mergeinfo information is already present in parent's mergeinfo.
That is, for example, if parent X mergeinfo has values x,y and z, the child of X doesn't need to maintain the x,y and z mergeinfo values.
That is, for example, if parent X mergeinfo has values x,y and z, the child of X doesn't need to maintain the x,y and z mergeinfo values.
