The Node.namespaceURI read-only property returns the namespace URI of the node, or null if the node is not in a namespace. When the node is a document, it returns the XML namespace for the current document.
::before creates a pseudo-element that is the first child of the element matched. It is often used to add cosmetic content to an element by using the content property. This element is inline by default.
The ::first-lineCSSpseudo-element applies styles only to the first line of an element. The amount of the text on the first line depends of numerous factors, like the width of the element, width of the document, and the font size of the text. As all pseudo-elements, ::first-line does not match any real HTML element.
The :hover CSS pseudo-class matches when the user designates an element with a pointing device, but does not necessarily activate it. This style may be overridden by any other link-related pseudo-classes, that is :link, :visited, and :active, appearing in subsequent rules. In order to style appropriately links, you need to put the :hover rule after the :link and :visited rules but before the :active one, as defined by the LVHA-order: :link — :visited — :hover — :active.
The :invalid CSS pseudo-class represents any <input> or <form> element whose content fails to validate according to the input's type setting. This allows you to easily have invalid fields adopt an appearance that helps the user identify and correct errors.
The :-moz-system-metric(windows-default-theme) CSS pseudo-class matches an element if the user is currently using one of the following themes in Windows: Luna, Royale, Zune, or Aero (i.e., Vista Basic, Vista Standard, or Aero Glass). This will exclude Windows Classic themes as well as third-party themes.
The :-moz-ui-invalid CSS pseudo-class represents any validated form element whose value isn't valid based on their validation constraints, in certain circumstances. This pseudo-class is applied according to the following rules: