@PipelineProperty(
            description = "The feed that output stream should be written to. If not specified the feed the input " +
                    "stream belongs to will be used.",
            displayPriority = 2)
    @PipelinePropertyDocRef(types = FeedDoc.TYPE)
    public void setFeed(final DocRef feedRef) {
        this.feedRef = feedRef;
    }
Joins text instances into a single text instance.
stroom-pipeline/src/main/java/stroom/pipeline/writer/RollingStreamAppender.java