The idea of viewing two versions of a document side by side and comparing them goes back at least as far as Nelson's 'Parallel Textface' (1971), in which equivalent text fragments, perhaps transposed, were connected by lines. Programmers are also used to comparing versions in this way, but it is not clear to me how the user is supposed to make sense of the interconnecting lines when the unit of comparison is a word rather than a line. Highlighting differences on its own is clearly insufficient, but if combined with synchronisation of the two windows – keeping the text on the left in line with the text on the right – this should be enough to prevent the user losing his or her way. In any case interconnecting lines are impossible in HTML windows, and one of the goals of Phaidros was to display multi-version texts in an ordinary web browser.
Comparing two versions of the Sibylline Gospel (© N. Brocca, 2008)
With this goal in view I have now added Twin View to the wiki, which highlights the differences between two texts. In the Sibylline Gospel example there are 36 versions. The total number of pairs that could be compared is thus (36*35)/2 = 630. Some of the rival programs, such as Juxta and Medite compare texts in real time, cacheing the results in case the same pairs of texts are compared again. But this doesn't work so well when there are more than a handful of versions. An MVD file has the advantage that any combination of versions can be displayed in equal time and the comparison results don't need to be cached. So even if there are 5,600 versions, as in the case of the Greek New Testament, you will always get a quick response.
The version of each window can be changed by choosing the desired version from its popup menu. Text on the left that does not appear in the version on the right is highlighted red, and extra text on the right, not found in the left, is highlighted blue. As yet, transpositions are not detected – they will be shown as insertion/deletion pairs instead. Also, synchronisation has not yet been added, but as in the multilingual example, referenced at the start of this blog, synchronisation in HTML is possible by using hyperlinks to invisibly connect the left hand text with the text on the right. This should be added soon in a later update to the program.