[Tex2002ans]

<mark> is a new HTML5 element used for highlighting:

https://developer.mozilla.org/en-US/...L/Element/mark
https://www.w3.org/TR/html5/textleve...e-mark-element

<mark> is mostly used in-line. For example:

Spoiler:

<p>This is an example of <mark class="match">marked text</mark>.</p>

<p>And a “quote that is <mark>important</mark>.”</p>

After Pretty Printing in Sigil, each <mark> gets extra whitespace + placed on their own lines:

Spoiler:

  <p>This is an example of 

  <mark class="match">marked text</mark>

.</p>

  <p>And a “quote that is 

  <mark>important</mark>

.”</p>

In many cases, this extra whitespace can completely botch the spacing (especially around punctuation).

The actual display before Pretty Print:

This is an example of marked text.

And a “quote that is important.”

After Pretty Print:

This is an example of marked text .

And a “quote that is important .”

For Pretty Printing, <mark> should probably be treated just like a <b> or <i> tag.