Optional Attributes in Data Files

Context: HL Kit … Kit Reference … Conventions Used in Reference Section 

Information that is defined through XML attributes and/or PCDATA blocks is always required by default. The exception is an entry that is specifically designated as optional. If an entry is optional, it will be clearly designated as such within its description, with the text "(Optional)" appearing before the type is given. An optional attribute will always specify the default value that is used if the attribute is left blank. Optional PCDATA blocks are always treated as empty by default.