strikethrough text on Stack Exchange

Question

How do I strike through text (i.e. cross out, or put a line through it) within the Stack Exchange environment?

NB: There are many questions about how to strikeout using different packages, but this question is specifically about how to do it here on this website or on Math.SE.

Answer 1

Formatting of posts can be done using the visual editor within Stack Exchange, Markdown and some HTML. The latter includes "the following safe, whitelisted subset of HTML tags":

<a>              - hyperlink.
<b>              - bold, use as last resort <h1>-<h3>, <em>, and <strong> are 
                   preferred.
<blockquote>     - specifies a section that is quoted from another source.
<code>           - defines a piece of computer code.
<del>            - delete, used to indicate modifications.
<dd>             - describes the item in a <dl> description list.
<dl>             - description list.
<dt>             - title of an item in a <dl> description list.
<em>             - emphasized.
<h1>, <h2>, <h3> - headings.
<i>              - italic.
<img>            - specifies an image tag.
<kbd>            - represents user input (usually keyboard input).
<li>             - list item in an ordered list <ol> or an unordered list <ul>.
<ol>             - ordered list.
<p>              - paragraph.
<pre>            - pre-element displayed in a fixed width font and and 
                   unchanged line breaks.
<s>              - strikethrough.
<sup>            - superscript text appears 1/2 character above the baseline 
                   used for footnotes and other formatting.
<sub>            - subscript appears 1/2 character below the baseline.
<strong>         - defines important text.
<strike>         - strikethrough is deprecated, use <del> instead.
<ul>             - unordered list.
<br>             - line break.
<hr>             - defines a thematic change in the content, usually via a 
                   horizontal line.

You can strikeout a piece of text using the <s>...</s> HTML tag pairs.

For more information, see How do I format my posts using Markdown or HTML?

Answer 2

It's possible to strikethrough a text on a post using <s>text</s>

It's not possible to strikethrough on the comment.

It's possible to strikethrough a text on a chat using ---text---.

Answer 3

There is a user script that adds a strikeout button to the stackexchange editor, see https://stackapps.com/q/3341 for instructions for installing.

With this script the editor will have additional buttons on the top right:

(animation taken from https://stackapps.com/a/7932)