nl_tokens: Set a value of undefined on all indices in the range from .. to where a prototype of obj has an element . I . e . shadow all prototype elements in that range .
pl_tokens: function ( obj , from , to ) { for ( var proto = % object_get_prototype_of ( obj ) ; proto ; proto = % object_get_prototype_of ( proto ) ) { var indices = IS_PROXY ( proto ) ? to : % GetArrayKeys ( proto , to ) ; if ( IS_NUMBER ( indices ) ) { // It's an interval. var proto_length = indices ; for ( var i = from ; i < proto_length ; i ++ ) { if ( HAS_OWN_PROPERTY ( proto , i ) ) { obj [ i ] = UNDEFINED ; } } } else { for ( var i = 0 ; i < indices . <mask> ; i ++ ) { var index = indices [ i ] ; if ( from <= index && HAS_OWN_PROPERTY ( proto , index ) ) { obj [ index ] = UNDEFINED ; } } } } }