Avaustunniste

Avaustunniste, in Finnish markup terminology, is the opening tag of an element in markup languages such as HTML and XML. It marks the beginning of an element and typically follows the syntax that includes the element name and optional attributes.

The opening tag is structured with a less-than symbol, the element name, optional attribute assignments, and a greater-than symbol. For example, in HTML the opening tag of a paragraph is <p>, and when an attribute is present it can look like <div class="container">. The information inside an opening tag describes the element and its properties, such as styling, behavior, or metadata.

In most markup languages, elements are defined by a pair: an opening tag (avaustunniste) and a corresponding closing tag (suljetustunniste). The content between these tags is the element’s content. Some elements are void or self-closing, meaning they do not have a separate closing tag, for example <img src="image.jpg" alt="image"/> in XML or HTML5-era practice. In HTML, certain elements are inherently self-closing or do not require a closing tag, such as <br> or <hr>, depending on the doctype and parsing rules.

Differences arise between HTML and XML. In XML, all elements must be properly closed, either with a separate closing tag or in a self-closing form <tag/>. In HTML, tag names are typically case-insensitive, and the necessity of a closing tag for non-void elements can be influenced by the document’s doctype and parsing rules. The concept of opening and closing tags is central to parsing, rendering, and DOM construction in web documents and many markup formats.