This is a built-in template used for replace text in GSP, e.g.
<html> <body> Hello! </body> </html>
with internationalized GSP custom tag usage, e.g.
<html> <body> <g:message code="HelloKey"/> </body> </html> .

The template is editable. Along with expressions allowed in GSP context, you can also use the predefined variables that will be then expanded into the corresponding values.

Predefined variables will take the following values:
${PROPERTY_KEY}		Property key name which is specified in the corresponding properties file.
${PROPERTY_VALUE}		Property value which is specified in the corresponding properties file. This is an original GSP text selection value.