Return the position of the first match
<boost/url/grammar/string_view_base.hpp>
constexpr
size_type
find_first_of(
    char const* s,
    size_type pos,
    size_type n) const noexcept;
See core::string_view::find_first_of
| Name | Description | 
|---|---|
| s | The characters to search for | 
| pos | The position to start searching from | 
| n | The number of characters to search for |