v6.1

• Updated details on the usage of the <termSuffix> of the <list> field: the read operation of the termination suffix needs to fail on invalid value, i.e. failOnInvalid property needs to be used.
• Added an example of referencing an inner field of the <optional> in another's <optional> field condition.
• Allow check the size of the sequence fields (<string>, <data>, <list>) in the <optional> field condition by using # character after the sibling reference one $.
• Allow check whether preceding <optional> field exists in another <optional> field condition by using ? character after the sibling reference one $.