Require elements with optional end tags to be explicitly closed

Rule ID:: no-implicit-close
Category:: Style
Standards:: HTML5

Some elements in HTML has optional end tags. When an optional tag is omitted a browser must handle it as if the end tag was present.

Omitted end tags can be ambiguous for humans to read and many editors have trouble formatting the markup.

Rule details

Examples of incorrect code for this rule:

<ul>
    <li>foo
    <li>bar
    <li>baz
</ul>

error: Element <li> is implicitly closed by sibling (no-implicit-close) at inline:2:6:
  1 | <ul>
> 2 |     <li>foo
    |      ^^
  3 |     <li>bar
  4 |     <li>baz
  5 | </ul>


error: Element <li> is implicitly closed by sibling (no-implicit-close) at inline:3:6:
  1 | <ul>
  2 |     <li>foo
> 3 |     <li>bar
    |      ^^
  4 |     <li>baz
  5 | </ul>


error: Element <li> is implicitly closed by parent </ul> (no-implicit-close) at inline:4:6:
  2 |     <li>foo
  3 |     <li>bar
> 4 |     <li>baz
    |      ^^
  5 | </ul>


3 errors found.

<p>lorem ipsum
<p>dolor sit amet

error: Element <p> is implicitly closed by sibling (no-implicit-close) at inline:1:2:
> 1 | <p>lorem ipsum
    |  ^
  2 | <p>dolor sit amet


error: Element <p> is implicitly closed by document ending (no-implicit-close) at inline:2:2:
  1 | <p>lorem ipsum
> 2 | <p>dolor sit amet
    |  ^


2 errors found.

<p>
    <div>lorem ipsum</div>
</p>

error: Element <p> is implicitly closed by adjacent <div> (no-implicit-close) at inline:1:2:
> 1 | <p>
    |  ^
  2 |     <div>lorem ipsum</div>
  3 | </p>


1 error found.

Examples of correct code for this rule:

<ul>
     <li>foo</li>
     <li>bar</li>
     <li>baz</li>
</ul>

<p>lorem ipsum</p>
<p>dolor sit amet</p>