Sharing: Default Pinterest method?

We've gone back and forth a bit on what the Pinterest sharing buttons do—does it load the multi-image select modal or choose a single image for a Pinner to use. There has been inconsistency on what the official vs unofficial buttons do.

Currently, we have a filter in place that can choose between the two options and defaults to the single image option.

I think the multiimage modal provides more flexibility to both the site owner and the user (e.g. blogs that include multiple "Pinterest-friendly" images in the post body).

Thoughts on changing the default to the multi-image modal?

@aduth @csonnek

The issue mentions a filter controlling Pinterest's single-image versus multi-image sharing behavior, but names no files or tests. Start by locating that filter and the existing Pinterest sharing entry point; done means the default behavior is agreed, changed consistently, and verified for both button variants.

Written by the indexing model from the issue text.