@Override
    public void setDocumentLocator(final Locator locator) {
        try {
            if (useOriginalLocator) {
                this.locator = locator;
            } else {
                this.locator = this;
            }

            if (validator != null) {
                validator.setDocumentLocator(this.locator);
            }
        } catch (final RuntimeException e) {
            unexpectedError("setDocumentLocator()", e);
        } finally {
            super.setDocumentLocator(locator);
        }
    }
This method tells filters that a stream is about to be parsed so that
they can complete any setup necessary.
stroom-pipeline/src/main/java/stroom/pipeline/filter/SchemaFilter.java