Flowed

Flowed refers to a text format designed to allow plain text to be reflowed across different display widths, improving readability on varied devices while preserving the plain-text nature of the content. It is most commonly associated with email and is formalized in RFC 3676 as “Format=Flowed,” published in 2004. The standard specifies how paragraphs, line breaks, and spacing should be interpreted by clients that wrap text for display.

In flowed text, paragraphs may be divided into lines that are not semantically significant. A soft line break is used to indicate that adjacent lines belong to the same logical line. A trailing space at the end of a line signals that the line continues, rather than representing a paragraph end. The delsp parameter (delsp=yes or delsp=no) controls how these trailing spaces are treated during reflow: delsp=yes means the trailing space is removed when the text is rewrapped, while delsp=no preserves the trailing space to maintain the visual break.

Usage and compatibility vary. Content-Type: text/plain; format=flowed is the formal indicator sent by some email clients to enable reflowing. Many modern clients implement format=flowed to improve reading on small screens, but compatibility is not universal. Some clients misinterpret or strip flowed formatting, which can lead to altered line breaks or paragraph boundaries, especially for quoted text or code blocks.

Flowed text aims to balance readability with the simplicity of plain text, though it is not always suitable for preformatted content. When exact line structure must be preserved, other formats or explicit non-flowing plain text may be preferred. See RFC 3676 for detailed specifications.