19. The computer program product according to claim 18 , the operations further including obtaining the second document data in response to the identifying the second document data.
19. The computer program product according to claim 18 , the operations further including obtaining the second document data in response to the identifying the second document data. 20. The computer program product according to claim 19 , wherein the obtaining further includes obtaining third document data identified by a second document-specifying character string in the text document data, the second document-specifying character string having no modification relation with the first character string.