Declare the options of the function f:

Verify that f is called with exactly one positional argument and known options:

Appropriate messages are issued if the arguments to f are invalid:

Check the arguments for a function that takes between 1 and 3 positional arguments:

Require at least 2 positional arguments:

Calling f with 1 argument is invalid:

Require exactly 3 positional arguments:

Allow "hidden" options that do not appear in Options[f]:

The option a0 is not a known option for f:

Allow the option named hidden as well as any option of Graphics to be set:

Treat unknown trailing options in positions min+1 though max as positional arguments rather than options for f:

The rule b2 is treated as a positional argument:

With the default "OptionsMode""Longest", a message is issued for unknown options:

A known option is still treated as an option for f with "OptionsMode""Shortest":

Treat all elements as positional arguments rather than options for f:

Define a function that takes two arguments:

Issue a message for any other number of arguments and return unevaluated:

The following evaluates normally:

With an incorrect argument count, a message is issued:

Define a function that calls a helper function if called with at most one argument:

When called with at most one argument, the helper function is called:

When called with more than one argument, f returns unevaluated and issues a message:

CheckArguments[f[…],…] issues a message for f and returns False for invalid input to f:

If f does not accept options, all arguments are assumed to be positional:

CheckArguments[…,{min,max}] will always treat the first min arguments as positional:

Here, even though b0 matches OptionsPattern[], it is treated as a positional argument:

If the rule b0 is given after the positional arguments, it is treated as an unknown option:

Trailing rules matching OptionsPattern[] are treated as options if they are known options to f:

This is true even if "OptionsMode""Shortest" is given:

An option specification that contains both known and unknown options generates a message:

In "OptionsMode""Shortest", a list with known and unknown options is treated as a positional argument if possible:

An unknown option past the maximum number of positional arguments still generates a message:

Only rules matching OptionsPattern[] can be valid option specifications:

The rule 12 does not match OptionsPattern[]:

Thus it is treated as a positional argument:

If 12 is given after the positional arguments, it is treated as an invalid option specification:

CheckArguments returns False when ArgumentsOptions returns Failure[…]:

All arguments at or before the minimum argument count are considered positional arguments:

IgnoreCaseTrue is treated as an argument despite being an option to StringCases:

CheckArguments does not check whether the option values are correct:

Infinity is not a valid value for Heads: