• Problems

  This line enable URL Rewriting . It must be enabled via the RewriteEngine directive! and if your .htaccess file is going to use rewrite rules, you should always include this line. Otherwise, you can’t be sure if its enabled or not. The string “on” is case insensitive.

When to use Expressions

You can use the expr attribute to set attribute values based on values in the data dictionary.
Examples

    <a expr:href='data:blog.homepageUrl'>Home</a>
    A home link with the blog's homepage url.
    <a expr:href='data:blog.homepageUrl + "feeds/posts/default"'>Posts RSS</a>
    A link with the blog's post RSS feed url. The ‘+' operator concatenates the two strings.
    <a expr:class='data:post.allowComments ? "comment" : "no-comment">Comment</a>
    A link with the class "comment" when comments are allowed, and "no-comment" when they are not. The ternary operator (?:) takes the given boolean value and picks the first value (after the ?) if the boolean is true, or the second value (after the :) if the boolean is false