ed is an 8-bit-clean, POSIX-compliant line editor.  It should work with
any regular expression package that conforms to the POSIX interface
standard, such as GNU regex(3).

The following compiler directives are recognized:
GNU_REGEX	- use with GNU regex(3)
DES		- use to add encryption support (requires crypt(3))
NO_REALLOC_NULL	- use if realloc(3) does not accept a NULL pointer
BACKWARDS	- use for backwards compatibility

The file `POSIX' describes extensions to and deviations from the POSIX
standard.

The ./test directory contains regression tests for ed. The README
file in that directory explains how to run these.

For a description of the ed algorithm, see Kernighan and Plauger's book
"Software Tools in Pascal," Addison-Wesley, 1981.