Tagged types (yes, still a bit more!)

• Syntax: tag type definition tag IMPLICIT type definition tag EXPLICIT type definition

Examples:

SpecialEncoding ::= [PRIVATE 8] EXPLICIT BIT STRINGBinaryFile ::= [APPLICATION 3] IMPLICIT OCTET STRINGResearch-division ::= [1] CHOICE {product-based [0] NULL, basic [1] NULL}

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This is a fairly simple slide, showing the application of a tag to a type definition with nothing following the tag, and with the EXPLICIT and IMPLICIT keywords following the tag.

The meaning of the keywords is fairly obvious - the tagging of the type is to be implicit (overriding the outermost tag in the tag-list) or explicit (adding a new outermost tag to the tag-list).

The only difficult bit is knowing when you are allowed to implicitly tag something (you are always allowed to explicitly tag anything), and knowing what the tagging is if there is no keyword (IMPLICIT or EXPLICIT) after the tag. This latter depends on the module defaults, and is discussed in the following slides.