Balanced brackets: every step of four inputs
============================================

input: {[()]}   firstMismatch = -1
  read '{' at 0: push '}'           waiting for (top first): }
  read '[' at 1: push ']'           waiting for (top first): ] }
  read '(' at 2: push ')'           waiting for (top first): ) ] }
  read ')' at 3: pop ')', matches   waiting for (top first): ] }
  read ']' at 4: pop ']', matches   waiting for (top first): }
  read '}' at 5: pop '}', matches   waiting for (top first): (empty)
  end of input: waiting for (empty) -> balanced

input: ([)]   firstMismatch = 2
  read '(' at 0: push ')'           waiting for (top first): )
  read '[' at 1: push ']'           waiting for (top first): ] )
  read ')' at 2: expected ']' -> NOT balanced

input: ())   firstMismatch = 2
  read '(' at 0: push ')'           waiting for (top first): )
  read ')' at 1: pop ')', matches   waiting for (top first): (empty)
  read ')' at 2: stack is empty, nothing to close -> NOT balanced

input: (()   firstMismatch = 0
  read '(' at 0: push ')'           waiting for (top first): )
  read '(' at 1: push ')'           waiting for (top first): ) )
  read ')' at 2: pop ')', matches   waiting for (top first): )
  end of input: waiting for ) -> NOT balanced, openers left over