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<sub> Subscript

Used to mark text that should appear lower than the baseline and slightly smaller; inferior or subscript text.
Attributes
arrange
specific-use

Multi-lang Attributes

lang-focus
lang-focus-custom
lang-group
lang-source
lang-source-custom
lang-translate
lang-variant
lang-variant-custom

Base Attributes

id
xml:base
xml:lang
Models and Context
May be contained in
<addr-line>, <aff>, <alt-title>, <article-title>, <attrib>, <award-id>, <bold>, <chapter-title>, <chem-struct>, <code>, <collab>, <collab-name>, <comment>, <compound-kwd-part>, <compound-subject-part>, <conf-theme>, <copyright-holder>, <copyright-statement>, <corresp>, <data-title>, <def-head>, <disp-formula>, <edition>, <element-citation>, <ext-link>, <fixed-case>, <funding-source>, <gov>, <inline-formula>, <inline-media>, <inline-supplementary-material>, <institution>, <italic>, <kwd>, <label>, <license-p>, <meta-value>, <mixed-citation>, <monospace>, <named-content>, <on-behalf-of>, <overline>, <p>, <part-title>, <preformat>, <product>, <related-article>, <related-object>, <resource-name>, <role>, <roman>, <sans-serif>, <sc>, <see>, <see-also>, <series>, <series-text>, <series-title>, <sig>, <sig-block>, <source>, <std>, <std-organization>, <strike>, <styled-content>, <sub>, <subject>, <subtitle>, <sup>, <supplement>, <support-source>, <target>, <td>, <term>, <term-head>, <textual-form>, <th>, <title>, <trans-source>, <trans-subtitle>, <trans-title>, <underline>, <verse-line>, <version>, <xref>
Description
Any combination of:
Content Model
<!ELEMENT  sub          (#PCDATA %emphasized-text;)*                 >
Expanded Content Model
(#PCDATA | email | ext-link | uri | inline-supplementary-material |
related-article | related-object | bold | fixed-case | italic | monospace | overline | roman |
sans-serif | sc | strike | underline | ruby | alternatives | inline-graphic | inline-media |
private-char | chem-struct | inline-formula | tex-math | mml:math | abbrev | index-term |
index-term-range-end | milestone-end | milestone-start | named-content | styled-content | fn |
target | xref | sub | sup)*
Tagged Samples
Expression in text 
... 
<fig id="f7" orientation="portrait" position="float">
 <label>FIG. 7.</label>
 <caption>
  <p>(2Si=O-H)<sup>+</sup> complex formation mechanism via three-fold 
   coordination of the O atom with subsequent H 1<italic>s</italic> level 
   lowering and extra electron donation to a DB in SiO<sub>2</sub> and to 
   the Si conduction band in the SiO<sub>2</sub>/Si interface, respectively.
   Electron excitation over to the SiO<sub>2</sub> conduction band denoted 
   by a symbol × is not allowed because the energy needed for excitation over 
   to SiO<sub>2</sub> conduction band is larger than the H 1<italic>s</italic> 
   level lowering.</p>
 </caption>
 <graphic orientation="portrait" position="float" xlink:href="f7"/>
</fig>
...
...
<p>This article by Peter Wilmshurst (10 October 1998, pp 996-9)
 used the incorrect abbreviation for inspired partial pressure of oxygen. 
 The abbreviation should have been Pi<sc>o</sc><sub>2</sub> 
 not Fi<sc>o</sc><sub>2</sub>.</p>
...
Subscript and superscript “stacked”
As displayed
../graphics/stack.jpg
Tagged
...
<body>
 <p>The <italic>Escherichia coli argU</italic> gene encodes a minor arginine
  tRNA, tRNA<sup arrange="stack">Arg</sup><sub arrange="stack">UCU</sub>,
  which corresponds to the rare codon AGA and possibly AGG ...</p>
 ...
</body>
...