I may be way off base here as I'm just getting started with Ruby, but
I think there is a typo in the section:
The sample search form is declared using ERB's expression tag <%= but
I think it should be an ERB code tag <%
The former gives a compile error ("syntax error, unexpected ')'"),
whereas the latter works just fine.
Happy to change the docs at github if someone can confirm that this
does in fact need correcting.