For example, in the following abbreviated test HTML:
<span>some text</span>
<script>println("whf")</script>
We would have to craft the expectation file to include the "some text"
segment, usually with some leading whitespace. This is a bit annoying,
and makes it difficult to manually craft expectation files.
So instead of comparing the expectation against the entire DOM inner
text, we now send the inner text of just the <pre> element containing
the test output when we invoke `internals.signalTextTestIsDone`.
This is a non-standard API that other browsers implement, which
highlights matching text in the current window.
This is just a thin wrapper around our find in page functionality, the
main motivation for adding this API is that it allows us to write tests
for our find in page implementation.
