Steps to reproduce

1. Imagine you don't know any wikitext
2. Open VE
3. Insert a template (like {{Infobox chemical element}})
4. Create or choose some named parameter (like hazard symbols)
5. Try to insert a template to that parameter, e.g. GHS icon (like hazard symbols = {{GHS health hazard}}) or child infobox (like hazard symbols = {{Infobox chemistry hazard ... }})

Expected behavior
There should be some possibility to nest templates into named parameters if the parameter should contain only a template

Current behavior
Without knowledge of wikitext there is no way to do this.