h3	String expressions

pre		defm "<some text>" [ + <value> ]
		defm '<some text>' [ + <value> ]
		
p	Strings cannot be stored in labels and therefore most string operations make no sense. Strings can just occur as a string literal, either enclosed in a pair of ''' or a pair of '"'. Whichever character is chosen it must not occur inside the string.
p	<b>Note:</b> special characters in string cannot be escaped with '\'. This syntax was (probably) invented later for the programming language 'C'.

pre		defm "say 'Hello!'",0
		defm 'say "Hello!"',0

p	Characters in the string are translated to the target system's character set if the assembler directive '#charset' was used to define one. Else the characters must be in range 0 to 255. If the character is not available in the target character set the assembler reports an error.

p	The last character of a string may be modified by a numeric operation, most commonly used is setting bit 7 of the last character:

pre		defm "foobar"+0x80

p	The following operators are allowed: '+', '-', '&', '|', '^'.

p	There are 4 predefined strings available in the 'defm' instruction:
	__date__, __time__, __file__ and __line__.