Defines variables in the template.

It takes one or multiple semicolon-separated variable definitions.

Making a shortcut to a long path:

            <div tal:define="destname path/to/existing/variable">…</div>

          

Defining more than one variable at the same time:

            <span tal:define="fname string:Paul; lname string:Dupond">…</span>

          

Each definition may start with global keyword which makes variable available everywhere later in the template and all macros. Global variables can be redefined.

            <span tal:define="global hello string:hello world"/><p tal:content="hello"/>
          

On the contrary, a local variable is only available inside the element it is defined in (and inside macros that are called in this element):

            <span tal:define="hello string:hello world"/><p tal:content="hello"/>
            <!-- will produce an undefined variable error -->
          

Creating a string inside the template:

            <span tal:define="destname string:some string" />

          

Defining a string containing another variable:

            <span tal:define="fname string:Paul; hello string:Hello $fname! Welcome to this page" />

          

A small trick which uses content of the element (useful if you need to define very complex value):

            <span tal:define="global hello">Hello ${fname}! Welcome to this page</span>

          

In above example, the <span> tag won't show up because it has no printable content ( hello variable grabs it) nor attributes.