Editing Applesoft BASIC (section)

===Extensions===
Applesoft BASIC can be extended by two means: the ampersand ({{mono|&amp;}}) command and the {{mono|USR()}} function. These are two features that call low-level machine-language routines stored in memory, which is useful for routines that need to be fast or require direct access to arbitrary functions or data in memory. The {{mono|USR()}} function takes one argument, and can be programmed to derive and return a calculated function value to be used in a numerical expression. {{code|&}} is effectively a shorthand for {{mono|CALL}}, with an address that is predefined. By calling routines in the Applesoft ROM, it is possible for ampersand routines to parse values that follow the ampersand. Numerous third-party commercial packages were available to extend Applesoft using ampersand routines.