OptionalElement

OptionalElement[patt]

is a grammar rules pattern object that represents 0 or 1 instances of patt.

OptionalElement[patt,default]

uses default if the element is not present.

Details

Examples

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Basic Examples  (2)

Allow certain words to be optional:

Supply a default value for a missing element:

Possible Issues  (1)

The default value evaluates immediately:

Use a sentinel for a dynamic default value:

Introduced in 2015
 (10.1)