Importing and exporting of symbols is a feature that is very useful when your project spans many source-files and for example you need to jump to a routine defined in another file.

Import/export commands

Command	Meaning
IMPORT (or XREF) label[,label,...]	This instructs the assembler to define label as if it were present in the current file but leave the address calculation to the linker.
EXPORT (or XDEF) label[,label,...]	The assembler will make label accessible to other files during the link process.
GLOBAL label[,label,...]	If label is defined during the assembly it will be exported, if not it will be imported. Handy (very!) for include-files.