A filter is a particular rule for an expression. Use a pipe | character when you want to include filters in the expression.
In case you don’t have the customer’s first name, you can display a fallback text by using the default filter. So, if the first name field has no value in the system, display friend instead. It looks like this.
{{ Contact.1|default('friend') }}
If you would like to have more filters for one expression in your HTML-based email, you can combine them easily. To show the value in upper case and still have a fallback text, type the following.
{{ Contact.1|default('friend') | upper}}
Using multiple filters within one placeholder is allowed. When using nested or multiple filtering, pay attention to the order of the filters, because certain filters need to be in a specific position to work as expected. One example for this is the raw filter.