Why does Sublime Text snippet work only at the last row?

Question

I'm trying to create my own snippet for Sublime Text 3. Here it is:

<snippet>
    <content><![CDATA[
// begin $1
.$1$2
// end $1
]]></content>
    <!-- Optional: Set a tabTrigger to define how to trigger the snippet -->
    <tabTrigger>di</tabTrigger>
    <!-- Optional: Set a scope to limit where the snippet will trigger -->
    <scope>source.pug, text.pug</scope>
</snippet>

but it works only at the last row of document. what's wrong?