Reordering superblanks

Currently there is a major problem with how formatting / superblanks interacts with word/chunk reordering in Apertium.

If the input is

<a id="foobar" href="http://example.com">Foo <b>bar</b>.</a>

and we want to reorder the words, we currently only reorder the words, and don't touch (or even look at) the blanks, since we don't want to mess up the html, so the output becomes

<a id="foobar" href="http://example.com">Бар <b>фоо</b>.</a>

but now the bold has shifted from source word "bar" to the target word that was "foo" in the input.

Ideally, the output should be

<a id="foobar" href="http://example.com"><b>Бар</b> фоо.</a>

Problems

All language pairs do this kind of thing:

$ echo '<i>Perro</i> <b>blanco</b>' |apertium es-en -f html
<i>White</i> <b>dog</b>

And those that don't, will at some point mess up whatever formatting they're given.

The problem is not only that we bold or italicise the wrong word, but also that it limits any possibility of accurately finding out which words were reordered during translation. This kind of reordering information would be useful for systems like Mediawiki's Content Translation (see discussion).

Possible solution

User:Tino Didriksen's post at http://comments.gmane.org/gmane.comp.nlp.apertium/3921 outlines a solution:

For each format, we need a list of inline tags; for HTML this would include <b>, <i> and so on.

Other tags, like <p> are treated as before, but inline tags stick with their words:

Given input string "<p><b><i>My sister lives</i> <u>in Wales</u></b></p>" you turn that into

    My <b><i>
    sister <b><i>
    lives <b><i>
    in <b><u>
    Wales <b><u>

Now on outputting, we can just put the inline tags on each word – this might mean some tags are unnecessarily duplicated, but that should be fine.

What we need to support something like this in Apertium:

1. Each deformatter needs a list of which tags need the inline treatment
2. Deformatters have to turn <p><b><i>foo</i> bar</b></p> into something like [<p>][{<b><i>}]foo [{<b>}]bar[</p>]
   • Can it be as simple as [{}] or does it have to be more complicated? As it is, {} is escaped in regular superblanks, so an unescaped {} inside [] would have special meaning.
   • Also, reformatters need to distribute the tags again; preferably merging consecutive tags, although that's probably not too important.
3. Pretransfer will have to distribute the tags as well, so [{<i>}]^foo<vblex>+bar<prn># fie$ turns into [{<i>}]^foo# fie<vblex>$ [{<i>}]^bar<prn>$
4. Transfer modules have to treat the inline-blanks differently from other superblanks
   • They should not be in the <b pos="N"/> elements, but probably be part of the <clip>
     • For example: <clip pos="2" part="blank"/> where "blank" is a special part (similar to lemh/lemq/whole/tags) and using "blank" as a def-attr leads to a compile-time error.
     • Note that if a word is deleted, we should be fine; removing an inline blank will not mess up HTML etc. If we insert a word, transfer rule writers are free to copy the clip part="blank" from surrounding words onto the newly created one, though whether this makes sense or not is probably hard to tell in advance.