Regex to disallow more than 1 dash consecutively

Question

1. How can I disallow -- (more than 1 consecutive -)? e.g. ab--c
2. - at the back of words not allow, e.g. abc-<

Answer 1

^(?!-)(?!.*--)[A-Za-z0-9-]+(?

Explanation:

^             # Anchor at start of string
(?!-)         # Assert that the first character isn't a -
(?!.*--)      # Assert that there are no -- present anywhere
[A-Za-z0-9-]+ # Match one or more allowed characters
(?