Is your feature request related to a problem? Please describe.
There is no way to pretty print a simdjson::dom::element to a string (or at least I did not find one). There is only a way to minify it to a string (or a stream).

Describe the solution you'd like
A function like to_pretty_string() or a configurable stream manipulator pretty or a stand-alone class PrettyPrinter. Wha

They should take single matcher during construction, and their match method should take a generic range, using the new generic matcher support.

Expected usage:

REQUIRE_THAT(get_keys(), AllMatch(KeyPattern({1, 2, 3})));
REQUIRE_THAT(get_numbers(), NoneMatch(IsOdd{}));
REQUIRE_THAT(get_strings(), AnyMatch(Contains("webscale") && !Contains("MongoDB")));

the matching semantics

The doc is great! Hoewever some areas are still missing.
C++11 intoduced raw string literals: https://en.cppreference.com/w/cpp/language/string_literal

It is useful in many different areas, like strings with quotes, multiline strings and for example windows paths without escaping backslashes:

const char win_path[] = R"(c:\some\unescaped\path)";

The same cppreference link als

Names map and input are exchanged mistakenly. By sense of Preconditions paragraph they have to be exchanged I suppose, because there is no problem when map and result coincide (in current context).

It would be a cool proof of concept to see Flecs running in the browser. As a first step towards this, the ecs_graphics project could be ported as it showcases the bare minimum for a game with graphics (input + rendering).

Link to example:
https://github.com/SanderMertens/ecs_graphics