1. A computer-implemented method for unsupervised structuring of a plurality of legacy documents comprising a part of a homogeneous collection from a common input document format reflecting a layout text lacking language mark-up tags to a structured document format employing language mark-up tags and more useful for document structure analyses comprising: using a computer processor, inputting the documents via an input device into a computer module for processing; fragmenting the input documents into a plurality of document content elements in accordance with a predetermined set of document attributes identifiable from the input document format wherein the attributes comprise language mark-up format tags identifying hierarchical positions of the context elements; clustering selective sets of the content elements having document attribute similarities comprising the language mark-up format tags; validating the clustered sets with reference to common textual properties and organizational content within the collection by analysis of textual content or form of the content elements, wherein the textual content or form of the documents validate the clustering by identity of text or order for avoiding human-supervised validating of the clustering; categorizing the clustered sets into predetermined categories comprising structured elements of the structured document format; and organizing the document content elements by hierarchical dependency from the predetermined categories, wherein the organized document elements comprise the desired structured document format wherein the clustering and categorizing is automatically effected for any type of legacy document within the collection; wherein the fragmenting comprises forming the document content elements as a recursive block, where the recursive block comprises a body, an optional head, and an optional tail, and where the body, optional head and optional tail contain either text or another recursive block.