If you do not specify a field, it will search in the content and properties. This is a shortcut for searching all properties of type content. Terms can not contain a whitespace.
Both of these queries will find any nodes with the word "banana" in any property of type d:content.
If the appropriate data dictionary definition(s) for the field supports both FTS and untokenized search, then FTS search will be used. FTS will include synonyms if the analyzer generates them. Terms cannot contain whitespace.