This request is the merging of two requests:  Want to flag misspelled
tags as mistakes, but print custom tags.

REQUEST #1
If javadoc encounters a doc-comment tag that it doesn't recognize, such as:

	* @sea java.lang.String

(which is obviously a typographical error), javadoc simply ignores the entire tagged paragraph and neither issues an error message nor includes the text of the paragraph in the output HTML file.

This behavior makes it very difficult for writers of doc comments to debug their work.  So unless the JLS *requires* this behavior (which would be a JLS bug, IMHO), javadoc should at least issue an error message.

REQUEST #2  (from 4039014)
Display custom tags rather than ignoring them.  In the following example,
@precondition should be printed with a bold subheading "Precondition"
with its text following it.

   public class X{
        /**
         * the custom tag is ignored
         * @return this tag is working
         * @precondition this one is not displayed in the doc
         */
        public String Test() {
                    return "test";
        }
   }