Composition of Two Functions then Determine the Domain

The video tutorial explains how to compose two functions, F and G, by plugging G of X into F of X. It demonstrates the process using the example where G of X is the square root of 1 minus X squared. The tutorial then discusses the domain of the resulting function, concluding that it includes all real numbers since there are no restrictions on the expression 1 minus X squared.

Are there any restrictions on the function 1 - X^2?

What is the domain of the function discussed?