Since there are as many different uses of these Tag Sets as there are users, “Best Practice” is an elusive concept, impossible to define for all users. But in many situations there are common practices and it is sometimes possible to explain several good practices, allowing an archive or publisher to determine if one of them fits their situation. This section contains tagging writeups, more extended than is appropriate for any one element, that offer such tagging advice and alternatives.
The <alternatives> element holds multiple, logically equivalent (substitutable) versions of the same information object. The typical case is a graphic (<graphic>) which is provided in multiple formats (such as a tif, a jpeg, and an SVG image). These various formats offer processing alternatives for use by production personnel or by software in presenting the work to the user. For example, a high-resolution tif image may be included and designated for use in printing while the same image, provided as a lower-resolution jpeg file may be designated for use in web display.
Other potential use cases include:
The <alternatives> element can be used everywhere that <graphic> and <media> are allowed. For example, <alternatives> can be used inside a <fig> as part of the large group of options that can be inside a Figure. (See Tagging Figures.) This example shows a single figure (“Figure 3”) with four processing alternatives—3 graphics in different image formats and one media file:
<fig id="Fig12a"> <label>Figure 3<label> <caption> <title>Large Poodles</title> </caption> <alternatives> <graphic xlink:href="poodle12.tif"/> <graphic xlink:href="poodle12.jpeg"/> <graphic xlink:href="poodle12.gif"/> <media mimetype="xyz" xlink:href="poodle-jump12"/> </alternatives> </fig>
Similarly, a table (<table-wrap>) may be provided in multiple formats: for example, the table below has three alternative formats: an XML-tagged table, the equivalent image file, and a textual version with the tabular look created by lines and spacing.
<table-wrap> <id> ... a DOI</id> <label>Table 6.</label> <alternatives> <table...>...an XHTML formatted table ...</table> <preformat>...a tabular form with spaces and tabs...</preformat> <graphic ...a jpeg of the same table/> </alternatives> <table-wrap-foot>...</table-wrap-foot> <attrib>...</attrib> <permissions> <copyright-statement>...</copyright-statement> </permissions> </table-wrap>
Within elements that need to contain alternatives but have mixed content rather than element content models (<disp-formula>, <chem-struct>), there may be an alternative that contains just text characters. For example, the alternatives may be an equation in MathML, a jpeg image of the equation, and a plain text equation for search. The <textual-form> element can be used inside <alternatives> to hold such plain text version alternatives. For example, a <textual-form> element might contain an equation such as a + b = c as an alternative to the same expression tagged as MathML.