RXf_SKIPWHITE is for split " ", which is special, *not* for split / /.
/* Flags indicating special patterns */
#define RXf_START_ONLY (1<<(RXf_BASE_SHIFT+19)) /* Pattern is /^/ */
-#define RXf_SKIPWHITE (1<<(RXf_BASE_SHIFT+20)) /* Pattern is for a split / / */
+#define RXf_SKIPWHITE (1<<(RXf_BASE_SHIFT+20)) /* Pattern is for a split " " */
#define RXf_WHITE (1<<(RXf_BASE_SHIFT+21)) /* Pattern is /\s+/ */
#define RXf_NULL (1U<<(RXf_BASE_SHIFT+22)) /* Pattern is // */
#if RXf_BASE_SHIFT+22 > 31