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─────PWB Extensions─────────────────────────────────────────────────────────
 
     Extension modules are similar to the dynamic-link libraries used by
     Microsoft Windows.
 
     Note the following points about extension modules:
 
       ■  An extension module has no function main (main is in PWB).
 
       ■  PWB calls the extension functions you make public (export). It
          can also use switches you define. You may have additional
          internal functions and data that your extension functions use
          but that PWB does not know about.
          See: ◄Writing Editing Functions►
 
       ■  Extension functions must call certain PWB internal functions
          to do basic editing tasks. These functions are termed
          "callbacks" because PWB calls your function, which then calls
          back into PWB. You use callback functions for most tasks in an
          extension function.
          See: ◄Extension Functions (Alphabetical List)►
               ◄Extension Functions (by Category)►
 
       ■  You can also use some C run-time library functions.
          See: ◄Calling C Run-Time Functions►
 
       ■  Extension modules are loaded at run time, either during the
          initialization of PWB or with the load switch.
          See: ◄Load Switch►
               ◄PWB Extension Autoload►
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