The HTML <output> element represents the result of a calculation or user action.
The class global attribute is a space-separated list of the classes of the element. Classes allows CSS and Javascript to select and access specific elements via the class selectors or functions like the DOM method document.getElementsByClassName.
The contextmenu global attribute is the id of a <menu> to use as the contextual menu for this element.
id
The id global attribute defines a unique identifier (ID) which must be unique in the whole document. Its purpose is to identify the element when linking (using a fragment identifier), scripting, or styling (with CSS).
The lang global attribute participates in defining the language of the element, the language that is non-editable elements are written in or the language that the editable elements should be written in. The tag contains one single entry value in the format defined in the Tags for Identifying Languages (BCP47) IETF document. If the tag content is the empty string the language is set to unknown; if the tag content is not valid, regarding BCP47, it is set to invalid.
The style global attribute contains CSS styling declarations to be applied to the element. Note that it is recommended for styles to be defined in a separate file or files. This attribute and the <style> element have mainly the purpose of allowing for quick styling, for example for testing purposes.
Microformats (sometimes abbreviated μF) are simple conventions used to embed semantics in HTML and quickly provide an API to be used by search engines, aggregators, and other tools. These small patterns of HTML are used for marking entities that range from fundamental to domain-specific information, such as people, organizations, events, and locations. 
This HTML reference describes all elements and attributes of HTML, including global attributes that apply to all elements.
The HTMLSelectElement.selectedIndex is a long that reflects the index of the first selected <option> element. The value -1 indicates that no element is selected.
The HTMLTrackElement.src property reflects the value of the <track> element's src attribute, which indicates the URL of the text track's data.
The NavigatorID interface contains methods and properties related to the identity of the browser.
<a>
The HTML Anchor Element (<a>) defines a hyperlink to a location on the same page or any other page on the Web. It can also be used (in an obsolete way) to create an anchor point—a destination for hyperlinks within the content of a page, so that links aren't limited to connecting simply to the top of a page.
The HTML <abbr> element (or HTML Abbreviation Element) represents an abbreviation and optionally provides a full description for it. If present, the title attribute must contain this full description and nothing else.
The HTML Acronym Element (<acronym>) allows authors to clearly indicate a sequence of characters that compose an acronym or abbreviation for a word. This element has been removed in HTML5. Use <abbr> element.
The HTML <bdi> Element (or Bi-Directional Isolation Element) isolates a span of text that might be formatted in a different direction from other text outside it.
The HTML <bdo> Element (or HTML bidirectional override element) is used to override the current directionality of text. It causes the directionality of the characters to be ignored in favor of the specified directionality.
The HTML element line break <br> produces a line break in text (carriage-return). It is useful for writing a poem or an address, where the division of lines is significant.
The HTML <button> Element represents a clickable button.
The HTML <caption> Element (or HTML Table Caption Element) represents the title of a table. Though it is always the first descendant of a <table>, its styling, using CSS, may place it elsewhere, relative to the table.
The HTML Citation Element (<cite>) represents a reference to a creative work. It must include the title of a work or a URL reference, which may be in an abbreviated form according to the conventions used for the addition of citation metadata.