Trigger specs cache indentation fix + documentation & tests

[Telroshan]

Description

Following up on #1540

1. Indentation fix, as @1cg had suggested in the linked PR,

is it possible to eliminate the whitespace changes here to make the actual change clearer and then submit a whitespace fix in a separate PR?

2. Added documentation & tests that I had omitted in the other PR

Testing

Added 2 tests

• One that evaluates the same trigger strings as the parses spec strings test, but enables the cache, and make sure the cache was indeed used, expecting it to hold the same keys count as the evaluated example specs list
• A second one that makes sure the cached specs are actually reused. It adds a dummy value to the evaluated specs, then evaluates trigger specs for a new element with the same trigger string, and makes sure the returned object is the same as the first one (i.e. was correctly cached and reused)

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded