Add metavariable types for the handling of single source code places

[elfring]

👀 Source code search approaches can occasionally be so precise that only a single source code place should be found.
💭 Thus corresponding case distinctions should become more relevant.

1. Repetition must not occur (as it could be handled together with the metavariable type “position”).
   Data structures (which can store more than one item) would not be needed.
2. Unwanted match attributes
   • The length of a match can become irrelevant.
   • A specific source code position can be constructed by a script rule.
     It would be helpful then to omit the specification of additional object properties.

🔮 How will chances evolve for such software adjustments?