I've never been the best with Regex, but here's a possible attempt:
const acceptableSequence = str => !/(?<!\+)\w|\w(?!\+)/.test(str);
EDIT: Misread the requirements, don't need to account for end and beginning of line characters as exceptions.
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I've never been the best with Regex, but here's a possible attempt:
JavaScript
EDIT: Misread the requirements, don't need to account for end and beginning of line characters as exceptions.