1. Adjust incorrect explaining comment about regex.

2. Remove | from regex character classes

| means the literal | and not alternation, i.e. [a|b] means "a, | or b".
On the other hand in groups (a|b) means "either a or b"

IMPORTANT

• If the PR touches the public API, the changes have been approved in a separate issue with the "api-approved" label.
• The code complies with the Coding Guidelines for C#.
• The changes are covered by unit tests which follow the Arrange-Act-Assert syntax and the naming conventions such as is used in these tests.
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