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<underline> Underline

Used to mark text that should appear with a horizontal line beneath it.

Usage/Remarks

This is normally a print consideration — not a matter for XML tagging — as underlining is frequently prohibited in online works, since it is a common “this is a link” signal.
Emphasis as a Toggle Switch
The @toggle attribute controls the behavior of this element. When the value of @toggle is set to “no”, the emphasized text remains in the requested style, no matter what the surrounding text does. When the value of @toggle is is “yes”, if the surrounding text is set to the same emphasis style, the text within this element will change to another emphasis style, so that the text will always be typographically distinct from its surroundings.
Using the element <italic> as an example, setting the @toggle attribute to “no” would mean that material marked as italics will always be italics, even in an italic context. In contrast, if the @toggle attribute is set to “yes” on the <italic> element, then if the formatting context imposes italics (whether due to another <italic> element, a stylesheet, some CSS, or other means), then the italics would be turned off within that context, making the emphasized text emphasized by contrast, but not italic..
Attributes
specific-use
toggle
underline-style

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-statement>, <corresp>, <data-title>, <def-head>, <disp-formula>, <element-citation>, <ext-link>, <fixed-case>, <funding-source>, <funding-statement>, <gov>, <inline-formula>, <inline-media>, <inline-supplementary-material>, <italic>, <kwd>, <label>, <license-p>, <meta-value>, <mixed-citation>, <monospace>, <named-content>, <on-behalf-of>, <overline>, <p>, <part-title>, <preformat>, <price>, <product>, <rb>, <related-article>, <related-object>, <resource-name>, <role>, <roman>, <sans-serif>, <sc>, <see>, <see-also>, <series>, <series-text>, <series-title>, <sig>, <sig-block>, <source>, <std>, <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>, <xref>
Description
Any combination of:
Content Model
<!ELEMENT  underline    (#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 Sample

Underlined text in a paragraph

...
<p>... Oligonucleotide primers for the amplification of TbH4 included
 5′-ATTAGGT<italic>CAT</italic><underline><italic>ATG</italic>
 </underline><bold>CACCATCACCATCACCAT</bold>ACGCAGTCGCAGACCGTGACGG and
 3′-TATAGG<italic>AAGCTT</italic>CTAATCCTCGGTGTAGAGCGCCTCG. XP-1 
 was amplified with 5′-CAATTA<italic>CAT</italic><underline>
 <italic>ATG</italic></underline><bold>CATCACCATCACCATCAC</bold>
 AACGACGGCGAAGGAACTGTGC and 3′-AACCTG<italic>GAATTC</italic>GTCCATGCTCACTTCGAC,
 and the 38-kDa antigen was amplified with 5′-CAATTA<italic>CAT</italic>
 <underline><italic>ATG</italic></underline><bold>CATCACCATCACCATCAC</bold>
 TGTGGCTCGAAACCACCGAGC and ...</p>
...