1. A text processing apparatus for use with a host processor capable of receiving, storing, and transmitting previously keyed text, the text including symbolic characters and text control characters, the text control characters including multi-character extended formatting commands affecting the format of a document, comprising a keyboard for entering text, means for receiving text from the host processor in text stream form, means coupled to said text stream receiving means for storing said text stream, including said control characters, in said data stream format, editing means connected for receiving keystroke signals from said keyboard and including means for modifying said text stream stored in said storing means in accordance with said keystroke signals on a keystroke-by-keystroke basis, and a display for displaying said stored text, wherein the improvement comprises, text segmenting means for dividing said received text stream into segments and for chaining said segments, each segment having a variable-length of text and having a predetermined maximum length of text, the area within the maximum length not occupied by text being designated a slack area, each segment having at most one extended formatting command therein and segments not having an extended formatting command therein having a slack area not containing data and therefor available for inserts, and formatting means for reading said segmented text stream from said text store and mapping the contents thereof onto said display and means in said editing means for invoking said formatting means when a text editing step has been completed.