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 com.* package in JRE 1.8.0_191 rt.jar. Java source codes are also provided.

⏎ com/sun/imageio/plugins/png/PNGMetadataFormatResources.java

/*
 * Copyright (c) 2001, 2005, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package com.sun.imageio.plugins.png;

import java.util.ListResourceBundle;

public class PNGMetadataFormatResources extends ListResourceBundle {

    public PNGMetadataFormatResources() {}

    protected Object[][] getContents() {
        return new Object[][] {

        // Node name, followed by description
        { "IHDR", "The IHDR chunk, containing the header" },
        { "PLTE", "The PLTE chunk, containing the palette" },
        { "PLTEEntry", "A palette entry" },
        { "bKGD", "The bKGD chunk, containing the background color" },
        { "bKGD_RGB", "An RGB background color, for RGB and RGBAlpha images" },
        { "bKGD_Grayscale",
          "A grayscale background color, for Gray and GrayAlpha images" },
        { "bKGD_Palette", "A background palette index" },
        { "cHRM", "The cHRM chunk, containing color calibration" },
        { "gAMA", "The gAMA chunk, containing the image gamma" },
        { "hIST", "The hIST chunk, containing histogram information " },
        { "hISTEntry", "A histogram entry" },
        { "iCCP", "The iCCP chunk, containing an ICC color profile" },
        { "iTXt", "The iTXt chunk, containing internationalized text" },
        { "iTXtEntry", "A localized text entry" },
        { "pHYS",
          "The pHYS chunk, containing the pixel size and aspect ratio" },
        { "sBIT", "The sBIT chunk, containing significant bit information" },
        { "sBIT_Grayscale", "Significant bit information for gray samples" },
        { "sBIT_GrayAlpha",
          "Significant bit information for gray and alpha samples" },
        { "sBIT_RGB", "Significant bit information for RGB samples" },
        { "sBIT_RGBAlpha", "Significant bit information for RGBA samples" },
        { "sBIT_Palette",
          "Significant bit information for RGB palette entries" },
        { "sPLT", "The sPLT chunk, containing a suggested palette" },
        { "sPLTEntry", "A suggested palette entry" },
        { "sRGB", "The sRGB chunk, containing rendering intent information" },
        { "tEXt", "The tEXt chunk, containing text" },
        { "tEXtEntry", "A text entry" },
        { "tIME", "The tIME chunk, containing the image modification time" },
        { "tRNS", "The tRNS chunk, containing transparency information" },
        { "tRNS_Grayscale",
          "A grayscale value that should be considered transparent" },
        { "tRNS_RGB",
          "An RGB value that should be considered transparent" },
        { "tRNS_Palette",
          "A palette index that should be considered transparent" },
        { "zTXt", "The zTXt chunk, containing compressed text" },
        { "zTXtEntry", "A compressed text entry" },
        { "UnknownChunks", "A set of unknown chunks" },
        { "UnknownChunk", "Unknown chunk data stored as a byte array" },

        // Node name + "/" + AttributeName, followed by description
        { "IHDR/width", "The width of the image in pixels" },
        { "IHDR/height", "The height of the image in pixels" },
        { "IHDR/bitDepth", "The bit depth of the image samples" },
        { "IHDR/colorType", "The color type of the image" },
        { "IHDR/compressionMethod",
"The compression used for image data, always \"deflate\"" },
        { "IHDR/filterMethod",
"The filtering method used for compression, always \"adaptive\"" },
        { "IHDR/interlaceMethod",
          "The interlacing method, \"none\" or \"adam7\"" },

        { "PLTEEntry/index", "The index of a palette entry" },
        { "PLTEEntry/red", "The red value of a palette entry" },
        { "PLTEEntry/green", "The green value of a palette entry" },
        { "PLTEEntry/blue", "The blue value of a palette entry" },

        { "bKGD_Grayscale/gray", "A gray value to be used as a background" },
        { "bKGD_RGB/red", "A red value to be used as a background" },
        { "bKGD_RGB/green", "A green value to be used as a background" },
        { "bKGD_RGB/blue", "A blue value to be used as a background" },
        { "bKGD_Palette/index", "A palette index to be used as a background" },

        { "cHRM/whitePointX",
              "The CIE x coordinate of the white point, multiplied by 1e5" },
        { "cHRM/whitePointY",
              "The CIE y coordinate of the white point, multiplied by 1e5" },
        { "cHRM/redX",
              "The CIE x coordinate of the red primary, multiplied by 1e5" },
        { "cHRM/redY",
              "The CIE y coordinate of the red primary, multiplied by 1e5" },
        { "cHRM/greenX",
              "The CIE x coordinate of the green primary, multiplied by 1e5" },
        { "cHRM/greenY",
              "The CIE y coordinate of the green primary, multiplied by 1e5" },
        { "cHRM/blueX",
              "The CIE x coordinate of the blue primary, multiplied by 1e5" },
        { "cHRM/blueY",
              "The CIE y coordinate of the blue primary, multiplied by 1e5" },

        { "gAMA/value",
              "The image gamma, multiplied by 1e5" },

        { "hISTEntry/index", "The palette index of this histogram entry" },
        { "hISTEntry/value", "The frequency of this histogram entry" },

        { "iCCP/profileName", "The name of this ICC profile" },
        { "iCCP/compressionMethod",
              "The compression method used to store this ICC profile" },

        { "iTXtEntry/keyword", "The keyword" },
        { "iTXtEntry/compressionMethod",
              "The compression method used to store this iTXt entry" },
        { "iTXtEntry/languageTag",
              "The ISO tag describing the language this iTXt entry" },
        { "iTXtEntry/translatedKeyword",
              "The translated keyword for iTXt entry" },
        { "iTXtEntry/text",
              "The localized text" },

        { "pHYS/pixelsPerUnitXAxis",
            "The number of horizontal pixels per unit, multiplied by 1e5" },
        { "pHYS/pixelsPerUnitYAxis",
            "The number of vertical pixels per unit, multiplied by 1e5" },
        { "pHYS/unitSpecifier",
            "The unit specifier for this chunk (i.e., meters)" },

        { "sBIT_Grayscale/gray",
            "The number of significant bits of the gray samples" },
        { "sBIT_GrayAlpha/gray",
            "The number of significant bits of the gray samples" },
        { "sBIT_GrayAlpha/alpha",
            "The number of significant bits of the alpha samples" },
        { "sBIT_RGB/red",
            "The number of significant bits of the red samples" },
        { "sBIT_RGB/green",
            "The number of significant bits of the green samples" },
        { "sBIT_RGB/blue",
            "The number of significant bits of the blue samples" },
        { "sBIT_RGBAlpha/red",
            "The number of significant bits of the red samples" },
        { "sBIT_RGBAlpha/green",
            "The number of significant bits of the green samples" },
        { "sBIT_RGBAlpha/blue",
            "The number of significant bits of the blue samples" },
        { "sBIT_RGBAlpha/alpha",
            "The number of significant bits of the alpha samples" },
        { "sBIT_Palette/red",
            "The number of significant bits of the red palette entries" },
        { "sBIT_Palette/green",
            "The number of significant bits of the green palette entries" },
        { "sBIT_Palette/blue",
            "The number of significant bits of the blue palette entries" },

        { "sPLTEntry/index", "The index of a suggested palette entry" },
        { "sPLTEntry/red", "The red value of a suggested palette entry" },
        { "sPLTEntry/green", "The green value of a suggested palette entry" },
        { "sPLTEntry/blue", "The blue value of a suggested palette entry" },
        { "sPLTEntry/alpha", "The blue value of a suggested palette entry" },

        { "sRGB/renderingIntent", "The rendering intent" },

        { "tEXtEntry/keyword", "The keyword" },
        { "tEXtEntry/value", "The text" },

        { "tIME/year", "The year when the image was last modified" },
        { "tIME/month",
          "The month when the image was last modified, 1 = January" },
        { "tIME/day",
          "The day of the month when the image was last modified" },
        { "tIME/hour",
          "The hour when the image was last modified" },
        { "tIME/minute",
          "The minute when the image was last modified" },
        { "tIME/second",
          "The second when the image was last modified, 60 = leap second" },

        { "tRNS_Grayscale/gray",
          "The gray value to be considered transparent" },
        { "tRNS_RGB/red",
          "The red value to be considered transparent" },
        { "tRNS_RGB/green",
          "The green value to be considered transparent" },
        { "tRNS_RGB/blue",
          "The blure value to be considered transparent" },
        { "tRNS_Palette/index",
          "A palette index to be considered transparent" },
        { "tRNS_Palette/alpha",
          "The transparency associated with the palette entry" },

        { "zTXtEntry/keyword", "The keyword" },
        { "zTXtEntry/compressionMethod", "The compression method" },
        { "zTXtEntry/text", "The compressed text" },

        { "UnknownChunk/type", "The 4-character type of the unknown chunk" }

        };
    }
}

⏎ com/sun/imageio/plugins/png/PNGMetadataFormatResources.java

Or download all of them as a single archive file:

File name: jre-rt-com-1.8.0_191-src.zip
File size: 8099783 bytes
Release date: 2018-10-28
Download 

⇒ Backup JDK 8 Installation Directory

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

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)