17. A machine for processing an electronic document, comprising computer hardware operable to perform operations comprising: extracting logical blocks from the electronic document including a text block comprising text lines each encompassed by a respective bounding rectangle; receiving the explicit logical blocks; extending edges of ones of the bounding rectangles to at least one boundary without changing layout relationships among the logical blocks in the electronic document; a text layout boundary from extended and unextended edges of the bounding rectangles; and storing a description of the text layout boundary in a machine-readable medium.
17. A machine for processing an electronic document, comprising computer hardware operable to perform operations comprising: extracting logical blocks from the electronic document including a text block comprising text lines each encompassed by a respective bounding rectangle; receiving the explicit logical blocks; extending edges of ones of the bounding rectangles to at least one boundary without changing layout relationships among the logical blocks in the electronic document; a text layout boundary from extended and unextended edges of the bounding rectangles; and storing a description of the text layout boundary in a machine-readable medium. 18. The machine of claim 17 , wherein the text layout boundary extraction engine is configured to identify at least one boundary to which ones of the bounding rectangles are extendable without changing layout relationships among logical blocks in the electronic document.