For the purpose of generating forms extrapolated from the schema a custom notation has been added to suggest the type of form control to use. "type": "string" would default to <input type="text" /> but you may override that with "type": "textarea" to suggest the use of a <textarea></textarea> form control.
JSON Schema supports designating multiple types; however, it may complicate implementation. The preferred design would be to either describe a more comprehensive object or to chose the more flexible type. For example, instead of using "type": ["integer", "string"] use "type": "string" as an number may be stored in a string but not visa versa.
However, I've been using "type": ["integer", "boolean"] to describe situations in which I want to differentiate false from 0 (zero). However, unless you require that accuracy false will be treated as 0 and 1+ will be treated as true.