NSAttributedString

NSAttributedString is a Cocoa and Foundation class that represents a string together with a collection of attributes that apply to ranges within the string. Each range carries a dictionary of attributes such as font, color, paragraph style, or links. The class is immutable; editing is performed with NSMutableAttributedString, a mutable subclass.

Attributes are specified with keys like NSFontAttributeName, NSForegroundColorAttributeName, NSParagraphStyleAttributeName, NSLinkAttributeName, and NSAttachmentAttributeName, among others. In Swift, these keys are surfaced as NSAttributedString.Key.font, .foregroundColor, .paragraphStyle, .link, and related constants.

An attributed string stores a single plain string plus one or more attribute dictionaries associated with ranges. You can query attributes at an index, enumerate attributes over a range, or modify a mutable attributed string with methods such as addAttribute:value:range:, replaceCharactersInRange:, or appendAttributedString:.

NSAttributedString supports initialization from a plain string or from serialized formats such as RTF or HTML via data initializers and document attribute options. It can be drawn and measured in user interfaces; supported rendering targets include UILabel, UITextView, NSTextField, NSTextView, and other drawing contexts. Methods like size, boundingRectWithSize:options:context:, and drawInRect enable layout and rendering.

This structure is commonly used to present rich text in apps, enabling per-range styling within a single string, embedding attachments, and handling interactions on links or other interactive attributes. The mutable variant provides the editing pathway, while the immutable form is typically used for passing around styled text within a program.