RTEditor/src/main/java/com/onegravity/rteditor/converter/tagsoup/Schema.java
public void attribute(String elemName, String attrName, String type,
                          String value) {
        ElementType e = getElementType(elemName);
        if (e == null) {
            throw new Error("Attribute " + attrName
                    + " specified for unknown element type " + elemName);
        }
        e.setAttribute(attrName, type, value);
    }
public void attribute(String elemName, String attrName, String type,
                          String value) {
        ElementType e = getElementType(elemName);
        if (e == null) {
            throw new Error("Attribute " + attrName
                    + " specified for unknown element type " + elemName);
        }
        e.setAttribute(attrName, type, value);
    }
Add or replace a default attribute for an element type in this schema.

@param elemName Name (Qname) of the element type
@param attrName Name (Qname) of the attribute
@param type     Type of the attribute
@param value    Default value of the attribute; null if no default