How to get cross-references descriptions?

Hi there! I'm currently trying to retrieve cross-reference descriptions from the ChEBI Ontology compounds. For example:

```xml

The potassium salt of diclofenac.
0
C14H10Cl2NO2.K
InChI=1S/C14H11Cl2NO2.K/c15-10-5-3-6-11(16)14(10)17-12-7-2-1-4-9(12)8-13(18)19;/h1-7,17H,8H2,(H,18,19);/q;+1/p-1
KXZOIWWTXOCYKR-UHFFFAOYSA-M
334.243
332.97257
O=C([O-])Cc1ccccc1Nc1c(Cl)cccc1Cl.[K+]
Beilstein:6625757
CAS:15307-81-0
DrugBank:DB00586
KEGG:D00903
PMID:1502708
potassium {2-[(2,6-dichlorophenyl)amino]phenyl}acetate
chebi_ontology
2-((2,6-dichlorophenyl)amino)benzeneacetic acid, monopotassium salt
Cataflam
CHEBI:4508

diclofenac potassium




Beilstein:6625757
Beilstein




CAS:15307-81-0
ChemIDplus




PMID:1502708
Europe PMC

```

I am expecting something like:
```python
frozenset({
Xref('ChemIDplus', 'CAS:15307-81-0'),
Xref('Europe PMC', 'PMID:1502708'),
Xref('Beilstein', 'Beilstein:6625757')
})
```
However, I am getting:
```python
frozenset({
Xref('CAS:15307-81-0'),
Xref('PMID:1502708'),
Xref('Beilstein:6625757')
})
```
It seems like Pronto might be having some trouble understanding the ontology cross-reference structure. I'm wondering if I might be doing something wrong? Could you please guide me on how to retrieve descriptions? Your assistance would be greatly appreciated! Thank you in advance for your help!