public Builder clearRegex() {
        regex_ = getDefaultInstance().getRegex();
        bitField0_ = (bitField0_ & ~0x00000002);
        onChanged();
        return this;
      }
<pre>
Optional. An regular expression hint.
</pre>

<code>string regex = 2 [(.google.api.field_behavior) = OPTIONAL];</code>

@return This builder for chaining.
java-visionai/proto-google-cloud-visionai-v1/src/main/java/com/google/cloud/visionai/v1/TagParsingConfig.java