Some built-in environment variables are available for use in a Dapp spec. They function in a similar way to constants in that they are constant, unchange-able values. The difference is that they are automatically available and do not have to be explicitly declared.
At present the following environment variables are available:
How to use
To refer to a constant, use the @env[name] syntax, where name is the the actual constant name. See the docs for inputs for examples.