## Expression

Writing the right rename expression is surely the most delicate part of Siren usage.

It expresses the way a new file name is constructed.
It can contain text (which is copied as it is) and variables which are replaced with the values they have for the file.

The folowing pages will describe you how to get the best of it :

- Variables : A complete list of available variables
- Modifiers : The modifications you can apply to a variable
- Date formats : Choose the way you want a date to be represented
- Advanced features

Two tools should help you :

| The Completion window lists all elements available for an expression. Double clicking on the one you're interested in will copy it in the expression text field.
| The Wizard offers an easier interface to create simple expressions.

Moreover you'll find in this help a lot of useful examples that you'll can copy/paste to Siren's "expression" field.