Assertion: expression's number | /r/HasProperty | valid
Facets:
Source sentences:
text: An expression is a syntactic construct, it must be well-formed: the allowed operators must have the correct number of inputs in the correct places, the characters that make up these inputs must be valid, have a clear order of operations, etc.
text: If the number is valid (matches the character sequence specified by the regular expression), the script shows a message thanking the user and confirming the number.