public String mapSafeAttribute(String elementName, String attributeName) {
        Set<String> safeAttrs = SAFE_ATTRIBUTES.get(elementName);
        if ((safeAttrs != null) && safeAttrs.contains(attributeName)) {
            return attributeName;
        } else {
            return null;
        }
    }
Normalizes an attribute name. Assumes that the element name
is valid and normalized
tika-parsers/tika-parsers-standard/tika-parsers-standard-modules/tika-parser-html-module/src/main/java/org/apache/tika/parser/html/DefaultHtmlMapper.java