1. An information processing apparatus for processing document data described in a structured language, the information processing apparatus, comprising: at least one processor configured to control a plurality of units, the plurality of units including, a storage unit configured to store at least a part of the document data, the document data having a plurality of nodes arranged in a tree structure, the tree structure having a plurality of levels, each node including an element of the part of the document data, an importance of each of the nodes being defined by a layer in the tree structure to which the node belongs; a parsing unit configured to parse the plurality of nodes on layer-by-layer basis in an order of decreasing importance in order to extract information contained in the elements of the part of the document data, wherein the parsing unit parses all nodes associated with a first layer before parsing nodes associated with a second layer, the first layer having a higher importance than that of the second layer, wherein, in response to a first instruction provided external to the parsing unit by a user, for a preferential parsing of a designated node, the parsing unit stores a current parsed position, temporarily interrupts the layer-by-layer basis parsing and preferentially parses a node under the designated node, the node under the designated node having an importance lower than an importance of the designated node, and in response to a second instruction for canceling the preferential parsing of the designated node, the second instruction provided external to the parsing unit by a user, the parsing unit resumes the layer-by-layer basis parsing by returning to the stored parsed position.