Several of the example managed-schema files have an outdated comment about docValues and StrField. In Solr 6.6.0 these are under solr-6.6.0/solr/server and the lines where the comment starts for each file are:
In the case of Solr-6.6.0/server/solr/configsets/basic_configs/conf/managed-schema, shortly after the comment are some lines which seem to directly contradict the comment:
216 <!-- The StrField type is not analyzed, but indexed/stored verbatim.
217 It supports doc values but in that case the field needs to be
218 single-valued and either required or have a default value.
On line 221 a StrField is declared with docValues that is multiValued:
221 <fieldType name="strings" class="solr.StrField" sortMissingLast="true" multiValued="true" docValues="true" />
Also note that the comments above say that the field must either be required or have a default value, but line 221 appears to satisfy neither condition.
The JavaDocs indicate that StrField can be multi-valued https://lucene.apache.org/core/6_6_0//core/org/apache/lucene/index/DocValuesType.html