Feature summary (what you would like to be able to do and where):
It is possible to specify suggested values in the TemplateData. Their support is implemented in the VisualEditor. Their use simplifies template customization and helps the user to understand it.

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):

• Try to insert any template with suggested values, for example, https://www.mediawiki.org/wiki/Template:Graph:PageViews - Interpolate parameter
• Add this parameter and tru to understand what it want :)

Benefits (why should this be implemented?):
Users will make fewer mistakes, and there will be no need to duplicate the proposed values in the parameter description.