anchor.diff:  They have no line number.
   They are available only in "run" mode.
   
  -BREAK
  -~~~~~
  -
  -Sets, clears, or displays breakpoints.
  -
  -Syntax: BREAK line-number
  -Syntax: BREAK -line-number
  -Syntax: BREAK
  -
  -To set a breakpoint, type 'BREAK' followed by a line number.
  -To clear a breakpoint, type 'BREAK' followed by a negative line number.
  -To display breakpoints, type 'BREAK' with no arguments.
  -
  -CROSSREF
  -~~~~~~~~
  -
  -Lists the numeric constants, text constants, functions, and variables used in the program, along with the line numbers on which they appear.
  -
  -DELETE
  -~~~~~~
  -
  -Removes lines from the program.
  -
  -My experience with other BASIC interpreters is that lines can be deleted by simply typing a line number and pressing RETURN.
  -(That is, entering an "empty" line with line number and nothing else.)
  -That technique does not work with BASIC-1965, as BASIC-1965 allows empty lines to be part of a program.
  -
  -So how to remove a line from a program?
  -Replacing a line with an empty line is possible, and certainly makes the offending line "go away" from execution, but what if we want to really remove a line?
  -
  -That's what the DELETE command does.
  -
  -DELETE uses the same specification as the LIST command.
  -
  -Syntax:	DELETE [line specification]
  -
  -If the list specification is a single line, it is deleted immediately.
  -If the list specification is a range, the lines are displayed and the user must confirm the operation.
  -
  -The DELETE command with no specification (implying the entire program) does not delete the program but does nothing.
  -(To delete the entire program, use the NEW command.)
  +LOAD
  +~~~~
  +
  +Loads a stored program into memory.
  +Sorts statements by line number.
  +Clears the current program prior to loading the new one.
  +
  +Syntax:	LOAD filename
  +
  +The 'filename' argument must be enclosed in quotes.
  +
  +Clears all breakpoints.
  +
  +SAVE
  +~~~~
  +
  +Saves the current program to disk.
  +Will overwrite an existing file without prompting.
  +
  +Syntax:	SAVE filename
  +
  +The 'filename' argument must be enclosed in quotes.
  +
  +NEW
  +~~~
  +
  +Clears the current program.
  +Does not ask to save a loaded program.
  +
  +Syntax:	NEW
  +
  +Clears all breakpoints.
   
   LIST
   ~~~~
  
positive.code: 
  The second phase executes statements, starting with the lowest-numbered statement and following the path of execution.
  
  SAVE
  ~~~~
  
  Saves the current program to disk.
  Will overwrite an existing file without prompting.
  
  Syntax:	SAVE filename
  
  The 'filename' argument must be enclosed in quotes.
  
  TOKENS
  ~~~~~~
  
negative.code: |LIST 100+ |Lists line 100 and the next 20 lines.
  |==========
  
  RUN
  ~~~
  
  