SED - Records, Buffers and Windows
A record to be edited is held in a buffer. Buffers may also hold records being created but not yet written to disk or other data such as lists of records in a file. SED allows use of up to 20 buffers.
The editor displays a window in which a number of lines of the record being edited can be seen at any one time. Where a line is wider than the display, the entire window pans from side to side to maintain the cursor within the display area.
The bottom two lines of the screen display status information. The upper status line shows the file and record names of the data being edited. If the data has been changed and hence does not match what is stored in the file, an asterisk is displayed at the start of this line.
The lower status line displays several status fields. From left to right these show
the number of lines in the record
the current cursor position (line and column, both numbered from one)
the status of macro collection
the state of insertion overlay mode
the state of indentation mode
the search mode
the count for repeated functions and operations with a numeric prefix
The lower status line is also used by some editor functions to request qualifying information. A limited set of editing functions can be used within this prompt area. These are forward char, back char, start line, end line, delete char, backspace, kill line and insert kill buffer. The kill line function used in this area deletes all characters after the cursor without affecting the kill buffer. The insert kill buffer function will insert the first line from the kill buffer at the current cursor position.
The display may optionally include line numbering. See the LNUM command for further details.