snippet with text transformation

i have this snippet

<snippet>

    <content><![CDATA[ \$${1:var}['${1}']['${3}'] ]]></content>

    <tabTrigger>var2</tabTrigger>

    <scope>text.html,source.php</scope>

    <description>$var['']['']</description>

</snippet>

and i want to text transform (Title case) this part['${1}'] while typing ${1:var}

so result should be like this

$adv['Adv']['name']

is it possable?