This tool is only available from ModelBuilder for use in models. The tool is not available from the Geoprocessing pane or from Python.
The tool has two Boolean outputs, True and False. Based on the condition being evaluated, one of the two Boolean outputs is true and the other is false after the tool runs. These Boolean outputs must be set as a precondition to the downstream tools for those to run if either of the preconditions is true.
The Expression parameter only supports Python expressions. Other scripting languages are not supported.
Use the Expression parameter for short one-line expressions. Use the Code Block parameter for more complicated expressions, such as multiline calculations or logical operations. The Code Block parameter cannot be used on its own; it must be used in conjunction with the Expression parameter.
Variables created in ModelBuilder can be used by this tool but cannot be connected directly to the Expression parameter. To use a variable in the expression, enclose the variable name in percent signs.
You cannot access model variables in the Code Block parameter. These variables must be passed on to the code block from the expression. To do this, create a function definition in the Code Block parameter and reference the Expression parameter value.
In Python, proper indentation is part of the syntax. The indentation level (two spaces or four spaces) does not matter as long as it is consistent throughout the code block.