how to append arbitrary string to yasnippet placeholder field

Question

I would like to know how to append a default string to a placeholder.

For example, I currently have:

# -*- mode: snippet -*-
# name: render template
# key: rt
# group: Flask
# contributor: Jon Rostran
# --
render_template("${0:index.html}")

But I would like for rt to expand to render_template("|.html") where the | is my cursor position after expansion.

Answer 1

Was making things harder than I thought. Solved it with this render_template("$0.html")

EDIT:

Explanation

The default expansion of render_template("${0:index.html}") is render_template("index.html"), but I would like to save myself from overriding "index.html" and manage typing the .html extension by default. Thus, render_template("$0.html") allows me to type only the name of the file so that after expansion I start typing here render_template("|.html"), without overriding and typing .html part again.