Define a default argument for a function f:

These are the defaults associated with f:

DefaultValues returns rules corresponding to default arguments for a function:

Create several values:

Obtain the default values of symbols whose names start with f:

DefaultValues can be used to set the values directly:

The resulting rules are in the order given:

Now reorder the definitions:

Copy a symbol's defaults to another symbol:

Assigning a value to Default[f] will define default arguments for all positions:

Assigning values to Default[f,i] will define default arguments for the i position:

Assigning values to Default[f,i,n] will define default arguments for the i position when f is called with n arguments:

Assigning values to Options[f] will define default options:

DefaultValues[f] only affects pattern matching for f:

It does not on its own create any transformation rules for f[…]:

Defaults can be defined by immediate or delayed assignments:

HoldPattern is used to protect the rules from their own definitions:

Without the HoldPattern, the left-hand side would have evaluated:

DefaultValues["sym"] will issue a message if the specified symbol does not exist:

If the symbol exists but has no definitions, an empty list is returned:

Definition and Information display defaults but do not return them as values:

DefaultValues returns a value that can be used in a program:

Use ClearAll to clear default values:

Clear does not clear them: