<p>When an authoring tool is used to edit a non-conforming document, it may preserve the

conformance errors in sections of the document that were not edited during the editing session

(i.e. an editing tool is allowed to round-trip erroneous content). However, an authoring tool

(i.e., an editing tool is allowed to roundtrip erroneous content). However, an authoring tool

must not claim that the output is conformant if errors have been so preserved.</p>

<p>Authoring tools are expected to come in two broad varieties: tools that work from structure

<div algorithm>

<p>The rules to <dfn>parse a global date and time string</dfn> are as follows. This will return

either a time in UTC, with associated time-zone offset information for round-tripping or display

either a time in UTC, with associated time-zone offset information for roundtripping or display

purposes, or nothing. If at any point the algorithm says that it "fails", this means that it is

aborted at that point and returns nothing.</p>

<p>If the resulting value is not a recognized language tag, then it must be treated as an unknown

language having the given language tag, distinct from all other languages. For the purposes of

round-tripping or communicating with other services that expect language tags, user agents should

roundtripping or communicating with other services that expect language tags, user agents should

pass unknown language tags through unmodified, and tagged as being BCP 47 language tags, so that

subsequent services do not interpret the data as another type of language description.

<ref>BCP47</ref></p>

<code>html</code> element and before the <code>head</code> element, will be dropped when the

document is parsed; <span>ASCII whitespace</span> <em>after</em> the <code>html</code> element

will be parsed as if it were at the end of the <code>body</code> element. Thus, <span>ASCII

whitespace</span> around the <span>document element</span> does not round-trip.</p>

whitespace</span> around the <span>document element</span> does not roundtrip.</p>

<p>It is suggested that newlines be inserted after the DOCTYPE, after any comments that are

before the document element, after the <code>html</code> element's start tag (if it is not <span

<ul class="domTree"><li class="t1"><code>html</code><ul><li class="t1"><code>head</code></li><li class="t1"><code>body</code><ul><li class="t1"><code>a</code></li><li class="t1"><code>a</code></li><li class="t1"><code>table</code></li></ul></li></ul></li></ul>

</div>

<p>For historical reasons, this algorithm does not round-trip an initial U+000A (LF) character in

<p>For historical reasons, this algorithm does not roundtrip an initial U+000A (LF) character in

<code>pre</code>, <code>textarea</code>, or <code>listing</code> elements, even though (in the

first two cases) the markup being round-tripped can be conforming. The <span>HTML parser</span>

first two cases) the markup being roundtripped can be conforming. The <span>HTML parser</span>

will drop such a character during parsing, but this algorithm does <em>not</em> serialize an extra

U+000A (LF) character.</p>

<!-- https://github.com/whatwg/html/issues/944 -->

<p>For <code>Element</code>s, if any of the elements in the serialization are in no namespace, the

default namespace in scope for those elements must be explicitly declared as the empty string.<!--

because otherwise round-tripping might break since it'll pick up the surrounding default ns when

because otherwise roundtripping might break since it'll pick up the surrounding default ns when

setting --> (This doesn't apply in the <code>Document</code> case.) <ref>XML</ref>

<ref>XMLNS</ref></p>