The Stack Exchange engine allows only the following safe, whitelisted subset of HTML tags:
Bold, use as last resort. <h1>–<h3>, <em>, and <strong> are preferred.
Specifies a section that is quoted from another source.
Defines a piece of computer code.
Delete, used to indicate modifications.
Describes the item in a <dl> description list.
Title of an item in a <dl> description list.
<h1> <h2> <h3>
Specifies an image tag.
Represents user input (usually keyboard input).
List item in an ordered list <ol> or an unordered list <ul>.
Pre-element displayed in a fixed width font and and unchanged line breaks.
Superscript text appears 1/2 character above the baseline. Used for footnotes and other formatting.
Subscript appears 1/2 character below the baseline.
Defines important text.
Strikethrough is deprecated, use <del> instead.
Defines a thematic change in the content, usually via a horizontal line.
<!-- [...] -->
Defines a comment, or text that will not be rendered in the post.
Note that since we allow the above HTML tags, to have tags show up as text you need to escape the < character. You can escape '<' by marking it as code (with indentation or backticks as is done below) or by using the HTML entity <.
Any tags not in the above list will be stripped out of the post. Do note that the sanitizer that strips out tags will recognize any text between < and > signs as HTML, and so any such text will be stripped out of the post; to prevent this, encode those signs as < and >. This does also mean that HTML comments cannot contain the > sign.
Attributes are only allowed on <img> and <a>. Other tags with attributes will be stripped.
Allowed attributes for img
The following attributes are allowed on the <img> tag, in the order shown below. Note that the mobile theme enforces a maximum width of 90%, so specifying a height might not scale the image proportionally on the mobile sites.
The attribute order is important! Using a different order (e.g., height before width) will strip the tag!
width="" (up to 999; do not include the px extension)
height="" (up to 999; do not include the px extension; see note above)
The following attributes are allowed on the <a> tag:
HTML tags unlisted above are stripped from the output. They may render in the client preview, but they will always be removed on the server.
You must enter the tags exactly as shown. Any deviation from this list other than capitalization: adding extra spaces, using apostrophes ' instead of quotation marks " or no quotes at all, means the tag will be stripped.
While it is possible to make tables using Markdown syntax, we do not support the HTML <table> element.