JRE 8 rt.jar is the JAR file for JRE 8 RT (Runtime) libraries. JRE (Java Runtime) 8 is the runtime environment included in JDK 8. JRE 8 rt.jar libraries are divided into 6 packages:

com.* - Internal Oracle and Sun Microsystems libraries
java.* - Standard Java API libraries.
javax.* - Extended Java API libraries.
jdk.* -  JDK supporting libraries.
org.* - Third party libraries.
sun.* - Old libraries developed by Sun Microsystems.

JAR File Information:

Directory of C:\fyicenter\jdk-1.8.0_191\jre\lib
      63,596,151 rt.jar

Here is the list of Java classes of the org.* package in JRE 1.8.0_191 rt.jar. Java source codes are also provided.

⏎ org/w3c/dom/html/HTMLElement.java

/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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/*
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 * Copyright (c) 2000 World Wide Web Consortium,
 * (Massachusetts Institute of Technology, Institut National de
 * Recherche en Informatique et en Automatique, Keio University). All
 * Rights Reserved. This program is distributed under the W3C's Software
 * Intellectual Property License. This program is distributed in the
 * hope that it will be useful, but WITHOUT ANY WARRANTY; without even
 * the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
 * PURPOSE. See W3C License http://www.w3.org/Consortium/Legal/ for more
 * details.
 */

package org.w3c.dom.html;

import org.w3c.dom.Element;

/**
 *  All HTML element interfaces derive from this class. Elements that only
 * expose the HTML core attributes are represented by the base
 * <code>HTMLElement</code> interface. These elements are as follows:  HEAD
 * special: SUB, SUP, SPAN, BDO font: TT, I, B, U, S, STRIKE, BIG, SMALL
 * phrase: EM, STRONG, DFN, CODE, SAMP, KBD, VAR, CITE, ACRONYM, ABBR list:
 * DD, DT NOFRAMES, NOSCRIPT ADDRESS, CENTER The <code>style</code> attribute
 * of an HTML element is accessible through the
 * <code>ElementCSSInlineStyle</code> interface which is defined in the  .
 * <p>See also the <a href='http://www.w3.org/TR/2000/CR-DOM-Level-2-20000510'>Document Object Model (DOM) Level 2 Specification</a>.
 */
public interface HTMLElement extends Element {
    /**
     *  The element's identifier. See the  id attribute definition in HTML 4.0.
     */
    public String getId();
    public void setId(String id);

    /**
     *  The element's advisory title. See the  title attribute definition in
     * HTML 4.0.
     */
    public String getTitle();
    public void setTitle(String title);

    /**
     *  Language code defined in RFC 1766. See the  lang attribute definition
     * in HTML 4.0.
     */
    public String getLang();
    public void setLang(String lang);

    /**
     *  Specifies the base direction of directionally neutral text and the
     * directionality of tables. See the  dir attribute definition in HTML
     * 4.0.
     */
    public String getDir();
    public void setDir(String dir);

    /**
     *  The class attribute of the element. This attribute has been renamed
     * due to conflicts with the "class" keyword exposed by many languages.
     * See the  class attribute definition in HTML 4.0.
     */
    public String getClassName();
    public void setClassName(String className);

}

⏎ org/w3c/dom/html/HTMLElement.java

Or download all of them as a single archive file:

File name: jre-rt-org-1.8.0_191-src.zip
File size: 951125 bytes
Release date: 2018-10-28
Download 

⇒ JRE 8 rt.jar - com.* Package Source Code

⇐ JRE 8 rt.jar - javax.* Package Source Code

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)