How to use regex in ElastAlert script filter?

Question

I'm trying to use regex in Painless script:

name: test

index: test-%Y.%m.%d
use_strftime_index: true

type: any


filter:
  - query:
      query_string:
        query: '
          (data.eventId: "4104" 
          AND _exists_: data.aux4)
          OR (data.eventId: "4103" 
          AND _exists_: data.aux8)
          OR (data.eventId: "800" 
          AND _exists_: (data.aux8 OR data.aux7))
        '
  - script:
      script:
        source: |
          def _scriptBlock = '';
        
          def test = /[a-z]/.matcher(doc["data.aux4.keyword"].value);
        
          if (doc['data.eventId.keyword'].value.contains('4104')) {
              _scriptBlock = doc['data.aux4.keyword'].value;
              SB = 'data.aux4.keyword';
          } else if (doc['data.eventId.keyword'].value.contains('4103')) {
              _scriptBlock = doc['data.aux8.keyword'].value;
          } else if (doc['data.eventId.keyword'].value.contains('800')) {
              if(doc["data.aux8.keyword"].size()>0){
                  _scriptBlock = doc['data.aux8.keyword'].value;
              }
              else {
                  _scriptBlock = doc['data.aux7.keyword'].value;
              }
          }
          return test.matches();
    

aggregation:
  minutes: 1

aggregation_key:
 - 'collector.organization'
 - 'eventSource.location.host'
 - 'subject.name'

out_es_index: test_ok

data.aux4 and other fields contains text data.

this script working, but there is no regex:

- script:
      script:
        source: |
          def _scriptBlock = '';
          
          def test = 'test';
          
          if (doc['data.msgId.keyword'].value.contains('4104')) {
              _scriptBlock = doc['data.aux4.keyword'].value;
          } else if (doc['data.msgId.keyword'].value.contains('4103')) {
              _scriptBlock = doc['data.aux8.keyword'].value;
          } else if (doc['data.msgId.keyword'].value.contains('800')) {
              _scriptBlock = doc['data.aux8.keyword'].value;
          }
          
          _scriptBlock.contains(test);

I'd tried to use .matches(), .find() - it didn't work. Using script filter because in future I'm going to add 40+ regex conditions in different fields.