Filter. Web.sitemap

[shapper]

Hello,

I have a Web.sitemap file where I added in each node the parameter
"footer" which I set to true or false.

I am creating a SiteMap datasource but I would like it to have only the
nodes where "footer" is set to "true".

I have no idea how to create this filter.

Could someone, please, help me?

Thanks,

Miguel