The <sub> element indicates that text should appear with subscript highlighting, or placed lower in relationship to the surrounding text. Subscripted text is often a smaller font than the surrounding text. Formatting might vary depending on your output process. This element is part of the highlighting domain. Use this element only when a more semantically appropriate element is not available.
Style sheets can be used to format the <sub> element differently, just like any other element can be restyled. Thus, it is not the case that content in <sub> elements will necessarily be rendered as subscript.
See appendix for information about this element in OASIS document type shells.
+ topic/ph hi-d/sub
<p>The power produced by the electrohydraulic dam was 10<sup>10</sup> more than the older electric plant. The difference was H<sub>2</sub>O.</p>