style - This attribute defines the styling language as a MIME type (charset should not be specified). This attribute is optional and defaults to text/css if it's missing. object - The content type of the resource specified by data. At least one of data and type must be defined. li - This character attribute indicates the numbering type:

• a: lowercase letters
• A: uppercase letters
• i: lowercase Roman numerals
• I: uppercase Roman numerals
• 1: numbers This type overrides the one used by its parent <ol> element, if any.

Usage note: This attribute has been deprecated: use the CSS list-style-type property instead. param - Only used if the valuetype is set to "ref". Specifies the MIME type of values found at the URI specified by value. source - The MIME-type of the resource, optionally with a codecs parameter. See RFC 4281 for information about how to specify codecs. button - The type of the button. Possible values are:

• submit: The button submits the form data to the server. This is the default if the attribute is not specified, or if the attribute is dynamically changed to an empty or invalid value.
• reset: The button resets all the controls to their initial values.
• button: The button has no default behavior. It can have client-side scripts associated with the element's events, which are triggered when the events occur. script -

Indicates the type of script represented. The value of this attribute will be in one of the following categories:

• Omitted or a JavaScript MIME type: For HTML5-compliant browsers this indicates the script is JavaScript. HTML5 spec urges authors to omit the attribute rather than provided a redundant MIME type. In earlier browsers, this identified the scripting language of the embedded or imported (via the src attribute) code. JavaScript MIME types are listed in the specification.
• module: HTML5 For HTML5-compliant browsers the code is treated as a JavaScript module. Processing of the script contents are not affected by the charset and defer attributes. For information on using module, see ES6 in Depth: Modules. 
• Any other value or MIME type: Embedded content is treated as a data block which won't be processed by the browser. The src attribute will be ignored.

Note that in Firefox you can use advanced features such as let statements and other features in later JS versions, by using type=application/javascript;version=1.8  . Beware, however, that as this is a non-standard feature, this will most likely break support for other browsers, in particular Chromium-based browsers.

For how to include exotic programming languages, read about Rosetta. link - This attribute is used to define the type of the content linked to. The value of the attribute should be a MIME type such as text/html, text/css, and so on. The common use of this attribute is to define the type of style sheet linked and the most common current value is text/css, which indicates a Cascading Style Sheet format. It is also used on rel="preload" link types, to make sure the browser only downloads file types that it supports. embed - The MIME type to use to select the plug-in to instantiate. ul - Used to set the bullet style for the list. The values defined under HTML3.2 and the transitional version of HTML 4.0/4.01 are:

• circle,
• disc,
• and square.

A fourth bullet type has been defined in the WebTV interface, but not all browsers support it: triangle.

If not present and if no CSS list-style-type property does apply to the element, the user agent decide to use a kind of bullets depending on the nesting level of the list.

Usage note: Do not use this attribute, as it has been deprecated; use the CSS list-style-type property instead. a - Specifies the media type in the form of a MIME type for the linked URL. It is purely advisory, with no built-in functionality. input - The type of control to render. See Form <input> types for the individual types, with links to more information about each. area - This attribute specifies the media type in the form of a MIME type for the link target. Generally, this is provided strictly as advisory information; however, in the future a browser might add a small icon for multimedia types. For example, a browser might add a small speaker icon when type is set to audio/wav. For a complete list of recognized MIME types, see https://www.w3.org/TR/html4/references.html#ref-MIMETYPES. Use this attribute only if the href attribute is present. ol - Indicates the numbering type:

• 'a' indicates lowercase letters,
• 'A' indicates uppercase letters,
• 'i' indicates lowercase Roman numerals,
• 'I' indicates uppercase Roman numerals,
• and '1' indicates numbers (default).

The type set is used for the entire list unless a different type attribute is used within an enclosed <li> element.

Note: This attribute was deprecated in HTML4, but reintroduced in HTML5. Unless the value of the list number matters (e.g. in legal or technical documents where items are to be referenced by their number/letter), the CSS list-style-type property should be used instead. menu - This attribute indicates the kind of menu being declared, and can be one of two values.

• context: Indicates the popup menu state, which represents a group of commands activated through another element. This might be as a button menu referenced by a menu attribute of a <button> element, or as context menu for an element with a contextmenu attribute. This value is the default if the attribute is missing and the parent element is also a <menu> element.
• toolbar: Indicates the toolbar state, which represents a toolbar consisting of a series of commands for user interaction. This might be in the form of an unordered list of <li> elements, or, if the element has no <li> element children, flow content describing available commands. This value is the default if the attribute is missing. menuitem - This attribute indicates the kind of command, and can be one of three values.
• command: A regular command with an associated action. This is the missing value default.
• checkbox: Represents a command that can be toggled between two different states.
• radio: Represent one selection from a group of commands that can be toggled as radio buttons.