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Symbols

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    Reserved symbols (null, true/false, empty, blank, first, last, size, etc.) and where they can be used.

    Symbols refer to an idea rather than to a specific object. Some may be used in place of an object (null, true/false) while others may only be used in a conditional (blank, empty) or as an object property. null and empty are documented on this page.

    The remaining reserved names are not types:

    true or false — The boolean values true and false. May be used anywhere a boolean is used. See also boolean under Simple Object Types.

    blank — In a conditional, tests for a null value, the boolean false, an empty string, a string containing only whitespace, or an empty list.

    key or value — Property names for the key or value of a dictionary pair. Not commonly used.

    first or last — On a list, the first or last item (null if the list is empty). If the object already has a property with that name (for example a custom field), that property wins.

    size — On a list, the number of items. If the object already has a property named size, that property wins.

    null

    An object with no value — a placeholder, like a missing chair at a table or the food on an empty plate. Written null or nil. May be used anywhere an object is used, but methods or filters that require a value can behave unexpectedly.

    empty

    The empty string (""). In a conditional, empty also matches an empty list. Used alone, empty evaluates as true; with is_valid it evaluates as false.