Guidelines for defining a fixed group

Each component must be a group with a fixed syntax or a fixed item. The item is padded to a fixed size or its minimum and maximum content size are equal.
Each component must have a specified range maximum. The maximum cannot be s.
If a component range minimum is not equal to the maximum, content is not required for optional component occurrences. For example, if a component is the item ShippingAddress (0:1) and ShippingAddress has a minimum content size of two characters, data may either contain: 1) all pad characters, or 2) if content is in the data stream, there must be a minimum of two characters for a ShippingAddress. If a component is a group, no content is required for any of the items contained in an optional occurrence of that component.