In the initialization function for the shared library that defines the new tag, register the tag using the function shtml_add_tag. The signature is:
| NSAPI_PUBLIC int shtml_add_tag (
    const char* tag,
    ShtmlTagInstanceLoad ctor,
    ShtmlTagInstanceUnload dtor,
    ShtmlTagExecuteFunc execFn,
    ShtmlTagPageLoadFunc pageLoadFn,
    ShtmlTagPageUnLoadFunc pageUnLoadFn);
          | 
Any of these arguments can return NULL except for tag and execFn.