Overview
An underline is a visible line placed immediately beneath characters to mark or emphasize text. It is one of the oldest methods of drawing attention to words and appears in handwriting, print, typewritten documents, and on screens. Underlining can signal emphasis, indicate links in hypertext, represent blanks to be filled, or serve decorative and organizational roles in layout.
Forms and styles
Underlines come in several visual variants and can be applied to whole words, phrases, or single characters. Common styles include:
- Solid single line — the most familiar and widely used form.
- Double or multiple lines — used for stronger emphasis or typographic effect.
- Dotted and dashed — often decorative or used in forms.
- Wavy lines — frequently used to indicate spelling or grammar issues in proofing software.
History and development
Underlining originated as a scribal and compositoral practice to note emphasis or to mark passages for later correction. With typewriters the underline became common because italics were unavailable. In print typography, underlining was less favored because it can obscure letterforms, especially descenders. In digital typography and web design, underlining is implemented by markup and style rules and remains familiar to many users because of its association with hyperlinks.
Digital implementation and semantics
On the web and in word processors, underlines are applied using formatting features or style rules. In HTML there is a specific element historically associated with underlining; modern best practice distinguishes visual styling from semantic meaning. Cascading Style Sheets allow fine control over line position and style. Designers commonly avoid underlining plain body text because underlines can be mistaken for links and may reduce legibility.
Practical uses and considerations
Typical uses include:
- Hyperlinks: underlines remain a key affordance to show clickable text in many interfaces.
- Forms and legal documents: underlines mark blanks or draw attention to required fields or signatures.
- Editorial and proofreading marks: different underline styles can flag various corrections.
Important considerations are readability and visual clutter. Underlines can collide with descenders (letters such as g, j, p) and make small text harder to read. They can also conflict with other text decorations like strikethroughs or highlights. For these reasons, designers often prefer alternatives for emphasis.
Alternatives and accessibility
Alternatives to underlining include italics, bold, color contrasts, and background highlighting. When underlines are used on the web, ensure that color alone is not the only cue for meaning and that links are distinguishable by more than color to assist users with color-vision differences. For accessible documents, clear semantic markup and consistent visual cues improve usability.
Notable facts: the visual convention of underlining links dates from the early web and remains widely recognized; however, typographers often discourage underlining body text for long passages because of its potential to reduce legibility.