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MessageName

symbol::tag

is a name for a message.

Details

You can specify messages by defining values for symbol::tag.
symbol::tag is converted to MessageName[symbol,"tag"]. tag can contain any characters that can appear in symbol names. symbol::"tag" can also be used.
Assignments for s::tag are stored in the Messages value of the symbol s.
The f::usage message is typically defined for functions intended for general use, giving a description of how to use the function.
?f prints out the message f::usage.
When ?form finds more than one function, only the names of the functions are printed.
You can switch on and off messages using On[s::tag] and Off[s::tag].
MessageName[symbol,"tag","lang"] or symbol::tag::lang represents a message in a particular language.

Examples

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Basic Examples (2)

Define a usage message for a function:

Show the usage message:

Process messages generated during an evaluation:

Scope (1)

Define a function that will test another function and give the argx message if needed:

Define g to use the test and return unevaluated when it fails:

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