|Function: Is STREAM known to be positioned at the beginning of a line? It is permissible for an implementation to always return NIL. This is used in the implementation of FRESH-LINE. Note that while a value of 0 from STREAM-LINE-COLUMN also indicates the beginning of a line, there are cases where STREAM-START-LINE-P can be meaningfully implemented although STREAM-LINE-COLUMN can't be. For example, for a window using variable-width characters, the column number isn't very meaningful, but the beginning of the line does have a clear meaning. The default method for STREAM-START-LINE-P on class FUNDAMENTAL-CHARACTER-OUTPUT-STREAM uses STREAM-LINE-COLUMN, so if that is defined to return NIL, then a method should be provided for either STREAM-START-LINE-P or STREAM-FRESH-LINE.