Implementation

TextEdit replaced the text editor of previous Macintosh operating systems, SimpleText. TextEdit reads and writes documents in Rich Text Format (RTF), Rich Text Format Directory, plain text, and HTML formats, and can open (but not save) old SimpleText files. It also has access to the operating system's built-in spell-checking service. The version included in Mac OS X v10.3 added the ability to read and write documents in Word format, and the version in Mac OS X v10.4 the ability to read and write Word XML documents. The version included in Mac OS X v10.5 includes read and write support for Office Open XML and OpenDocument Text. The version included in Mac OS X v10.6 added automatic spelling correction, support for data detectors, and text transformations. The version included in Mac OS X v10.7 includes versioning of files, and Autosave similar to iOS.

Formatted text, justification, and even the inclusion of graphics and other multimedia elements are supported by TextEdit, as well as the ability to read and write to different character encodings, including Unicode (UTF-8 and UTF-16). TextEdit automatically adjusts letter spacing in addition to word spacing while justifying text. This letter spacing feature is usually only found in higher-end desktop publishing programs. The unique letter spacing however can't be adjusted or controlled as it can in a desktop publishing program. TextEdit does not support multiple columns of text.

The high-resolution TextEdit 1.5 icon found in Mac OS X versions starting with 10.5 (Leopard) features an extract from Apple's "Think Different" ad campaign.