public void setPageSeparator(String pageSeparator) {
        if (pageSeparator.isBlank()) {
            return;
        }
        Matcher m = ALLOWABLE_PAGE_SEPARATORS_PATTERN.matcher(pageSeparator);
        if (!m.find()) {
            throw new IllegalArgumentException(pageSeparator + " contains illegal characters.\n" +
                    "If you trust this value, set it with setTrustedPageSeparator");
        }
        setTrustedPageSeparator(pageSeparator);
        userConfigured.add("pageSeparator");
    }
The page separator to use in plain text output.  This corresponds to Tesseract's
page_separator config option.
The default here is the empty string (i.e. no page separators).  Note that this is also
the default in
Tesseract 3.x, but in Tesseract 4.0 the default is to use the form feed control character.
We are overriding
Tesseract 4.0's default here.

@param pageSeparator
tika-parsers/tika-parsers-standard/tika-parsers-standard-modules/tika-parser-ocr-module/src/main/java/org/apache/tika/parser/ocr/TesseractOCRConfig.java