I'd reword this... how about something like:

```
The `output_to_stdout` and `output_to_stderr` matcher(s) provides a way to assert that
the supplied block has emitted content to either `stdout` or `stderr`.

With no argument the matcher asserts that there has been output, when you pass a
string then it asserts the output is equal (`==`) to that string and if you pass a regular
expression then it asserts the output matches it.

For example:

```Ruby
expect { puts "Some content" }.to output_to_stdout
expect { warn "Specifc content" }.to output_to_stderr('Specific content')
expect { warn "Specifc content" }.to output_to_stderr(/content/)
```.

```