Roundtripping Alternate Content

Office Open XML defines a mechanism for the storage of content which is not defined by this Office Open XML specification, for example extensions developed by future software applications which leverage the Open XML formats. This mechanism allows for the storage of a series of alternative representations of content, of which the consuming application may use the first alternative whose requirements are met.

Consider an application which creates a new paragraph property intended to make the colors of its text change randomly when it is displayed. This functionality is not defined in this Office Open XML specification, and so the application might choose to create an alternative representation setting a different manual color on each character for clients which do not understand this extension using an <AlternateContent> block as follows:

<ve:AlternateContent xmlns:ve="…">
  <ve:Choice Requires="colors" xmlns:colors="urn:randomTextColors">
    <w:p>
      <w:pPr>
        <colors:random colors:val="true" />
      </w:pPr>
      <w:r>
        <w:t>Random colors!</w:t>
      </w:r>
    </w:p>
  </ve:Choice>
  <ve:Fallback>
    <w:p>
      <w:r>
        <w:rPr>
          <w:color w:val="FF0000" />
        </w:rPr>
        <w:t>R</w:t>
      </w:r>
      <w:r>
        <w:rPr>
          <w:color w:val="00FF00" />
        </w:rPr>
        <w:t>a</w:t>
      </w:r>
      …
    </w:p>
  </ve:Fallback>
</ve:AlternateContent>

The <Choice> element that requires the new color extensions uses the <random> element in its namespace, and the <Fallback> element allows clients that do not support this namespace to see an appropriate alternative representation.

These alternate content blocks may occur at any location within a WordprocessingML document, and applications shall handle and process them appropriately (taking the appropriate choice).

However, WordprocessingML does not explicitly define a set of locations where applications shall attempt to store and roundtrip all non-taken choices whenever possible.

If an application does not understand the colors extension, the resulting file (if alternate choices are to be preserved would appear as follows:

<ve:AlternateContent xmlns:ve="…">
  <ve:Choice Requires="colors" xmlns:colors="urn:randomTextColors">
    …
  </ve:Choice>
  <ve:Fallback>
    …
  </ve:Fallback>
</ve:AlternateContent>

The file would then appear as follows after the choice is processed:

<w:p>
  <w:r>
    <w:rPr>
      <w:color w:val="FF0000" />
    </w:rPr>
    <w:t>R</w:t>
  </w:r>
  <w:r>
    <w:rPr>
      <w:color w:val="00FF00" />
    </w:rPr>
    <w:t>a</w:t>
  </w:r>
  …
</w:p>