MSPBlock

MSPBlock[{var_i,…},body]

interprets the argument variables and replaces them in body.

MSPBlock[{var_i,…},body,defvalue]

returns defvalue if any of the variables do not have values.

Details

This is one of the key ways to work with variables from the HTTP request.
MSPBlock takes each of the variables var_i, interprets them and then replaces any occurrences in body with the interpreted value.
If any variables do not have values, an empty string is returned.
The following exceptions can be thrown by MSPBlock:

	MSPException["ParseError"]	if the value cannot be interpreted by the Wolfram Kernel
	MSPException["SecurityError"]	if the value does not pass the security test
	MSPException["ValueError"]	if the value is not a string; this indicates a programmatic error by the page author
	MSPException["VariableError"]	if the variable is not a Wolfram Language symbol; this indicates a programmatic error by the page author

You can simulate how the functions work by loading the package and setting the security content:

Here, the variable $$var is assigned the value "5+7"; note that the value is a string:

When MSPBlock evaluates, all occurrences of $$var are replaced by its interpreted value:

If the input value cannot be interpreted, an MSPException is thrown:

If the input value does not pass the security test, an MSPException is thrown:

Input can also be given in MathML:

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