The isset() function always results in true, thus it is useless. If passed as argument variable is not set, the interpreter will throw an error.

include/ph7int.h

@@ -1594,7 +1594,6 @@ enum ph7_expr_id {
 #define PH7_KEYWORD_INCLUDE      41 /* include */
 #define PH7_KEYWORD_EMPTY        42 /* empty */
 #define PH7_KEYWORD_INSTANCEOF   0x400 /* instanceof: MUST BE A POWER OF TWO  */
-#define PH7_KEYWORD_ISSET        43 /* isset */
 #define PH7_KEYWORD_PARENT       44 /* parent */
 #define PH7_KEYWORD_PRIVATE      45 /* private */
 #define PH7_KEYWORD_FOR          48 /* for */