Returns a reference to the element by its ID; the ID is a string which can be used to identify the element; it can be established using the id attribute in HTML, or from script.
Returns a nodelist collection with a given name in the (X)HTML document.
Returns the <head> element of the current document. If there are more than one <head> elements, the first one is returned.
document.images returns a collection of the images in the current HTML document.
Returns a string containing the date and time on which the current document was last modified.
The Document.location read-only property returns a Location object, which contains information about the URL of the document and provides methods for changing that URL and loading another URL.
The Document.onfullscreenchange property is an event handler for the fullscreenchange event that is fire when a document goes in or out of the fullscreen mode.
The Document.onfullscreenerror property is an event handler for the fullscreenchange event that is fire when a document goes that cannot go in fullscreen mode, even it has been requested.
Returns the preferred style sheet set as set by the page author.
Returns a list of the <script> elements in the document. The returned object is an HTMLCollection.
The Document.visibilityState read-only property returns the visibility of the document, that is in which context this element is now visible. It is useful to know if the document is in the background or an invisible tab, or only loaded for pre-rendering. Possible values are:
The HTML <link> element specifies relationships between the current document and an external resource. Possible uses for this element include defining a relational framework for navigation. This Element is most used to link to style sheets.
JavaScript is designed on a simple object-based paradigm. An object is a collection of properties, and a property is an association between a name (or key) and a value. A property's value can be a function, in which case the property is known as a method. In addition to objects that are predefined in the browser, you can define your own objects. This chapter describes how to use objects, properties, functions, and methods, and how to create your own objects.
document.designMode controls whether the entire document is editable. Valid values are "on" and "off". According to the specification, this property is meant to default to "off". Firefox follows this standard. The earlier versions of Chrome and IE default to "inherit". Starting in Chrome 43, the default is "off" and "inherit" is no longer supported. In IE6-10, the value is capitalized. 
Gets/sets the domain portion of the origin of the current document, as used by the same origin policy.
Returns the height of the document object. In most cases, this is equal to the <body> element of the current document.