Important notes

Element assignment:
Atoms in the system are not automatically assigned elements by groan_rs unless the elements are explicitly specified in the input structure file. This is because elements may not always be meaningful, particularly in coarse-grained systems.
Using element keywords:
To use element name or element symbol in your selections, ensure that atoms have been assigned elements.
Assigning elements:
- From topology files: Creating the System structure from a TPR file automatically assigns elements.
- Guessing elements: Use the System::guess_elements function to assign elements based on atom names.
Recommendation:
If you're using a program that utilizes GSL, ensure that it assigns elements to atoms before using element keywords in selections.

Operator and parenthesis separation:
Operators (and, or, not, etc.) and parentheses do not need to be separated by whitespace unless it affects query clarity.
Valid example:
```
not(name CA)or(serial 1to45||Protein)
```
A valid query without (unnecessary) whitespace.
Invalid example:
```
not(name CA)or(serial 1to45orProtein)
```
Invalid because orProtein is unclear.
Resolving ambiguity:

Enclose ambiguous parts in parentheses to clarify intent. Or use whitespace, it is worth it.
```
not(name CA)or(serial 1to45or(Protein))
```
Now, the query is valid and interpretable, but not very human-readable.

GSL guide