question: @ Nullable String findLongestNamePrefix ( Node name , Set < String > namespaces ) { if ( namespaces . contains ( name . getQualifiedName ( ) ) ) { return name . getQualifiedName ( ) ; } else if ( name . isGetProp ( ) ) { return findLongestNamePrefix ( name . getFirstChild ( ) , namespaces ) ; } return null ; }
target:  Gets the longest namespace that is a prefix of the name node. Returns null if no namespaces are valid prefixes.