In Learn -> Using Pattern Matching, in the "Using the Pattern Variable" section, there are typos:

The following code checks if object is an instance of the String class, and if it is a non-empty string.

Here, "object" should be "o" as in the code example.

Later on in the same section:

If your code can execute the if branch and can carry one with the rest of the method, then the pattern variable is not created.

Here, "carry one" should be "carry on" (the spelling mistake makes it sound like it is doing maths! :-) ).