Lookup named submatch.

import std.regex;
import std.range;

auto c = matchFirst("a = 42;", regex(`(?P<var>\w+)\s*=\s*(?P<value>\d+);`));
assert(c["var"] == "a");
assert(c["value"] == "42");
popFrontN(c, 2);
//named groups are unaffected by range primitives
assert(c["var"] =="a");
assert(c.front == "42");