1. A method of providing meta-data associated with tree-structured data using a processing device, the method comprising: receiving in a first computer process of the processing device a meta-data query condition and threshold value indicating a desired level of access to a plurality of elements of the tree-structured data; traversing in a second computer process of the processing device non-leaf nodes of an index structure associated with the tree-structured data in accordance with indicators representing searchable ranges of explicit and inherited meta-data levels stored in the non-leaf nodes that satisfy the received meta-data query condition and threshold value from a root non-leaf node of the index structure until reaching a plurality of leaf nodes of the index structure, the searchable ranges of descendant non-leaf nodes being subsets of searchable ranges of ancestor non-leaf nodes and indicating meta-data levels available to access in leaf nodes of the index data structure that are associated with elements of the tree-structured data; and returning in a third computer process of the processing device one or more elements and their associated explicit or inherited meta-data levels indicated in the plurality of leaf nodes when the explicit or inherited meta-data levels of the one or more elements satisfy the received meta-data query condition and threshold value.