In GSP the <%= %> syntax introduced earlier is rarely used due to the support for GSP expressions. It is present mainly to allow ASP and JSP developers to feel at home using GSP. A GSP expression is similar to a JSP EL expression or a Groovy GString and takes the form ${expr}:

<html>
  <body>
    Hello ${params.name}
  </body>
</html>

However, unlike JSP EL you can have any Groovy expression within the ${..} parenthesis. Variables within the ${..} are not escaped by default, so any HTML in the variable's string is output directly to the page. To reduce the risk of Cross-site-scripting (XSS) attacks, you can enable automatic HTML escaping via the grails.views.default.codec setting in grails-app/conf/Config.groovy:

grails.views.default.codec='html'

Other possible values are 'none' (for no default encoding) and 'base64'.