Implement Balanced Parentheses

Allscripts Sunrise Clinical Manager may process text expressions containing parentheses, square brackets, and curly braces. Write a function that returns True when every delimiter is correctly matched and nested, and False otherwise.

Ignore all characters that are not delimiters. An empty string or a string containing no delimiters is considered balanced.

Formal Specification

Implement is_balanced(text), where text is a string. Return a boolean:

1. Opening delimiters (, [, and { must be closed by the corresponding delimiter.
2. Delimiters must close in last-in, first-out order.
3. A closing delimiter without a matching opening delimiter makes the string invalid.
4. All opening delimiters must be closed by the end of the string.