some more documentation

README.md

@@ -4,6 +4,13 @@ A regex engine.
 ### Syntax
 The aim was to follow Vim's regex syntax. Esoteric special characters such as "\zs" are not implemented, however the just is supported.
 
+```C
+match_t * regex_match(const regex_t * const regex, const char * const string, const bool start_of_string);
+```
+Returns a sentinel terminated array of `match_t` objects.
+The sentinel object is defined as `(match_t){ .position = -1, .width = -1, };`.
+The position and width of non-sentinel `match_t`s is guaranteed to be => 0.
+
 | Symbol | Meaning (TODO: fill in) |
 | :----: | :---------------------: |
 | .      | |