Final answer:
In JSP, you cannot nest <%--style comments within one another, as this will cause a compilation error. However, it is legal to embed expressions within directives. Proper use of these elements ensures the correct compilation and execution of the JSP page.
Step-by-step explanation:
The question asks about the legality of embedding comments and expressions within different elements in JavaServer Pages (JSP). Specifically, whether it is legal to nest a <%--style comment within another comment, and if it is legal to embed an expression inside a directive.
In JSP, <%--style comments are used to add comments that are not sent to the client. You cannot nest these comments within each other, as it would be considered invalid syntax and result in a compilation error. Alternatively, it is legal to embed an expression within a directive, as JSP allows this flexibility. Directives are used to give directions to the JSP container and can include JSP expressions that can later be evaluated.
It is important to use these elements correctly to ensure that the JSP page compiles and executes as expected.