HyperText Markup Language

- Layout Engine

Chrome Edge Firefox IE Opera Safari
Blink
Gecko
MSHTML (Trident)
WebKit

- HTML5

Link type "stylesheet" [1]

stylesheet
The default type for resources given by the stylesheet keyword is text/css.

The script element [1]

async
The async and defer attributes are boolean attributes that indicate how the script should be evaluated. Classic scripts may specify defer or async, but must not specify either unless the src attribute is present. Module scripts may specify the async attribute, but must not specify the defer attribute.
defer
The defer attribute may be specified even if the async attribute is specified, to cause legacy web browsers that only support defer (and not async) to fall back to the defer behavior instead of the blocking behavior that is the default.
type
The default, which is used if the attribute is absent, is "text/javascript".

The style element [1]

type
The default value for the type attribute, which is used if the attribute is absent, is "text/css".

Void elements [1] [2]

area, base, br, col, embed, hr, img, input, link, meta, source, track, wbr

- XHTML1.0

Element Prohibitions [1]

a
must not contain other a elements.
pre
must not contain the img, object, big, small, sub, or sup elements.
button
must not contain the input, select, textarea, label, button, form, fieldset, iframe or isindex elements.
label
must not contain other label elements.
form
must not contain other form elements.

- HTML4.01

How to specify alternate text [1]

alt
The alt attribute must be specified for the IMG and AREA elements. It is optional for the INPUT and APPLET elements.

Tabbing navigation [1]

tabindex
The following elements support the tabindex attribute: A, AREA, BUTTON, INPUT, OBJECT, SELECT, and TEXTAREA.

The INPUT element [1]

value
This attribute specifies the initial value of the control. It is optional except when the type attribute has the value "radio" or "checkbox".

The SCRIPT element [1]

defer
When set, this boolean attribute provides a hint to the user agent that the script is not going to generate any document content (e.g., no "document.write" in javascript) and thus, the user agent can continue parsing and rendering.
charset
Note that the charset attribute refers to the character encoding of the script designated by the src attribute; it does not concern the content of the SCRIPT element.

- Conditional Comments (IE9-) [1]

- Viewport [1]

- X-UA-Compatible [1] [2] [3]