“Underlying data provider ONLY supports AND-ing of clauses”

In Customer and Orders Manager source code we see following interesting comment
—
File: ProfilesSearchHelper.cs
Method:
public SearchClause CreateSearchCriteria(string profileType, SearchClauseFactory searchClauseFactory, SearchCriteriaItems criteriaList, bool isSimpleSearch)
—

SearchClause fullClause = CreateClause(searchClauseFactory, criteriaList[0]);
for (int i = 1; i < criteriaList.Count; i++)
{
if (!string.IsNullOrEmpty(criteriaList[i].Condition) && !string.IsNullOrEmpty(criteriaList[i].FieldName) && !string.IsNullOrEmpty(criteriaList[i].Value))
{
SearchClause rightClause = CreateClause(searchClauseFactory, criteriaList[i]);
// Underlying data provider ONLY supports AND-ing of clauses.
fullClause = searchClauseFactory.IntersectClauses(fullClause, rightClause);
}
}