a partial Java application program designed to run inside the womb of a web browser, with help from some predefined support classes.
Applet Difficulties
java.applet.Applets must run inside a web browser (or AppletViewer). You can also run them in Java Web Start to
avoid the peculiarities of individual browsers. You cannot run them from the java.exe command line. To spawn a web browser from within an application to get it to display an Applet,
see the tips under HTML rendering. Applets are typically automatically downloaded over the web freshly every time
they are executed. They can also be run from local hard disk. In contrast, applications cannot be run inside a browser, though it is possible to make a dual mode
program that can run either as an Applet or application. Applets run on the client’s machine. In contrast, Servlets
run on the host webserver.
Applets are harder to write than applications. I would recommend that beginners start with applications. With Applets you
have the following complications:
- Your entire logic must fit in the straight jacket of four methods init, start, stop and destroy.
- Unsigned (ordinary) Applets are restricted in hundreds of not-well-documented ways. They are not even allowed to read files.
- An Applet must run inside a browser. This adds an extra level of complication and uncertainty as different browsers have different bugs.
- Unless you spin off a separate Thread, an Applet has no mechanism to do any calculation that takes more than a fraction of a second.
The big appeal of Applets to the beginner is that you can post your handiwork on the web for everyone to play with and admire.
The easiest way to write an Applet is to start with a working one, perhaps one of mine. Write it as a hybrid,
and debug it as an application. Once you have it working as an application, test it as as Applet in a browser. If you have an IDE like Intellij
Idea, you can run it in the IDE as an Applet as an intermediate phase between testing as an application and as an Applet in a browser.
Unsigned Applet Restrictions
To make Applets very safe to run, even when they were composed by teens with the morals or skill of Beavis and Butthead, Applets
are severely restricted. Unsigned Applets (without special permission to bypass security) are not permitted to:
- talk to any server but the one you were loaded from. No talking to strangers. If they were loaded from a local disk, they can’t talk to any webserver at all. They
can’t load classes, read files, or have socket communications with any webserver but mom, the server htey were loaded from. Applets can send/receive
email to/from a different host, but only via the home host.
- I have discovered by experiment that when an Applet runs locally, it is only allowed to read files in the same directory or in a subdirectory of
that directory. It can’t read files in the parents or sibling directories, just child/grandchild directories. Oddly, it does not matter where the jar itself is, but
where the web page is that has the <applet tag. The files the Applet reads have to be “downstream” of
that page. You will notice multiple snippet subdirectories all over my website. This is because Applets could not get at a
central snippet directory. The place where I put the code snippets for a given webpage has to be in a branch off the directory containing the web
page. My only other alternative would be to always put the code snippets in the same directory as the web page. I am not sure if the same restriction applies to Applets
run on a webserver.
- I have not experimented with https:. Please let me know if you can use https in an unsigned Applet
and if you can mix http: to fetch the Applet jar and http: to fetch the data.
- I have discovered by experiment that when an Applet runs from a website, it is only allowed to read files in the same directory as the web page or
in a subdirectory of that directory, (downstream from the webpage). It can’t read files in the parents or sibling directories, just child/grandchild
directories. It does not matter where the jar is, just the web page and the files that you try to read. This means unsigned Applets usually end up
bundling everything they need to read as resources in the jar.
- read or write local files on the client machine. They are not even allowed to look in a directory or test for the existence of a file. You can however read a file (resource)
embedded in the jar with Class. getResource or Class.getResourceAsStream. It can
also read from the server via a URL. Even when your Applet is loaded from hard disk, it still may not do file I/O even via file:
URLs.
- Use System.setOut or System. setErr to redirect the console.
- Look at the restricted system properties, or get an enumeration of all the system properties. See Wassup. Don’t use Color.
getColor which interrogates the system properties.
- Monitor mouse motion.
- Print in JDK 1.1, though you can in JDK 1,2+. The user has to ok the printing though.
- Send email to a server other than the one it was loaded from.
- Talk to a serial port.
- Talk to a parallel port.
- Change thread priority, even lower it.
- Read or write the clipboard. However, users can manually cut/paste your AWT components without security clearance. The restriction is on programmatic control of the clipboard.
Swing components have no cut/paste ability at all.
- Install software.
- Execute any native code. If you use native JNI code, things get really complicated vis a vis security and signed Applets with native code.
You are better off to use Java Web Start.
- Exec external programs.
- Issue an RMI call to a remote object running on a different server than the Applet’s.
- Determine the structure of an object (fields, methods, values, etc.) using the Reflection API.
- Use the Preferences API to store or look at configuration information in the registry.
If your Applet needs to do any of the above things, it must be signed.
Now that IE has dropped Java, it is reasonable to ask your clients to upgrade to the latest Java, understanding that some will not. For them, you must develop or at least test
on earlier versions. Don’t just assume that just because you did not use any new features that you are home free.
Standalone Java applications are not so limited. Exactly what the limitations are is controlled by the security manager in the browser. If the user installs an alternate
security class, the Applet may have more powers. The security restrictions are controlled entirely by the browser. There is nothing to stop you from
writing a non-conforming browser that has quite different security restrictions for Applets. However, in practice, you write code to sign your jars
and bypass each of the five different security schemes used in browsers.
Programmers bitterly complain about these restrictions. The restrictions protect the end user from malicious web Applets they might encounter on the
web. Without such protection, vicious Applets could destroy the user’s hard disk, print reams of paper, phone out on a spare serial port and
rack up long distance bills, go sniffing on the LAN for the company books… You don’t want to give those powers to psychotic strangers — those same people
who stay up late at night writing viruses.
Applet Gotchas
- Don’t try to make Applets work on your website with naked class files. Always bundle everything, classes, gifs,
configuration scripts etc. up into a jar. This bypasses many classpath headaches, and it downloads faster. Further, the chances are much better your Applet
will work first time on the website once you get it working locally out of a jar.
- Applets are a pain in the behind. If you possibly can, use Java Web Start instead.
- Don’t try to use any of the Applet methods in your constructor such as getCodeBase. They depend on a private field
called appletStub that does not get initialised until just before your init method is called. You will get NullPointerExceptions
if you fail to heed this advice.
- Unsigned Applets are extremely restricted in what they can do. Carefully review the list above. In particular, Applets
cannot write to the local hard disk or talk to a server other than the one they were loaded from.
- AppletContext.getApplets will get all the Applets on the page, not just other instances of
the current class. Further, sometimes this instance is included, sometimes it is not. Don’t count on it working either way.
HTML to Invoke an Applet
I find it wise to sandwich the <applet…>… </applet> tags in <p> tags like this:
that stray-looking > is not a mistake. It has to be there to close the opening <applet tag This way the Applet
has lots of room to display. If you leave them, out your Applet may be rendered off the right edge of the screen, where you probably won’t see
it.
I repeat. Always bundle your
Applet (or
JApplet) classes and resources into a jar!
- You can then invoke your Applet from any page.
- The classes download faster.
- It is clear exactly which classes your Applet may use and not use.
- There are no classpath mysteries.
- It is always clear which version of the class files you are using.
- Everything just works more smoothly.
Here is tip to find the optimal size parameters. Run the Applet as an application. Drag the frame to the optimum size. Use Paint
Shop Pro to capture a screen snapshot of the frame, excluding the menu bar. Then look in the lower right corner of the PSP window to discover the size for the <applet
height and width tags. Then measure including the menu bar to discover the size for the Frame. setSize(
width, height ) when running as an application. It will need about 24 pixels extra height. This trick saves a lot of guesswork and experimentation to home in on the
optimal values.
When debugging Applets, remember to click Shift-Reload in your browser, not just plain Reload
to attempt re-running with your new version. Shift-Reload supposedly flushes the cache of class files. This usually does not work. You have to exit the browser and restart. It
is a good idea to put something unique in every incarnation of your code so you can tell if you are running the old or new code. I do it by flipping a background colour or
setting a micro version number.
You can go crazy debugging Applets because the browser sometimes caches old copies of jars, classes, html… It is best to start each test with
at least a fresh loading of your browser, preferably with all its caches deleted using a bat file before each test. I often start different a different browser for each test
to get a clean start, e.g. Opera, Firefox, SeaMonkey, Netscape, IE.
It is best to debug as an application, then at the last minute convert to an Applet.
Applet Tags
Applets are invoked to run in browsers by the <applet…> tag. Applets won’t work if you load them
directly with your browser as if they were web pages! The HTML commands for firing up an Applet are exceedingly picky. It matters whether you
have .class or not. I suggest you look at the files that come with the Conversion Amanuensis to see how to run an Applet/Application
with/without jars, locally, on a website, with various browsers and run times. Here is the basic structure:
| HTML Tag |
Comments |
|---|
| <applet |
| code= "MyClass.class" |
The name of the class file for the Applet. Make sure the case and name exactly match the name of the *.java file, *.class file, and class name.
For a class in a package this would have dots in it, e.g. com.mindprod.mypackage.Myclass.class , but it would not have any directory qualification.
You are not allowed to specify an absolute URL or absolute fully qualified hard disk filename. Strange as it sounds, you must specify the trailing .class,
though some browsers let you get away without it. All the Sun tutorials do it with the .class. If you leave it out, you will just get a gray square
with no error message, even if you have manifest Main-Class entry. |
| width= "330" |
width of entire Applet display in pixels. There is nothing the Applet can do itself to change this. If you needed
variable size you would have to resort to JavaScript or a server-side technology to generate HTML pages with the appropriate size. This can be specified as a percentage e.g. width="100%"
or with CSS commands. Then the Applet will grow and shrink with the enclosing window. |
| height= "240" |
height of entire Applet display in pixels. There is nothing the Applet can do itself to change this. |
| archive= "Everything.jar,Sub/MoreStuff.zip" |
Resource file, classes etc. Your ARCHIVE parameter must have a list of the absolute or relative jar files, separated by commas (no spaces). (Watch
out! The ARCHIVE tag in <OBJECT is space-separated!) If you have too little or too much qualification, or if you fail
to use the file naming conventions of your server, you will be in trouble. You are probably best to use absolute URLs or fully qualified hard disk file names. Whether the
archive is supposed to be relative to the current HTML directory, the CODEBASE, or all elements of the classpath is unclear. The forms of archive I
use most are archive="myapp.jar" archive="../myapp.jar" and archive="somedir/myapp.jar". |
| codebase= "http://mydomain.com/" |
I suspect CODEBASE is simply broken in the current implementations. Theoretically it is the absolute or relative URL/directory where class files are, like a one-element
classpath. Normally the class files are in the same directory as the html, so you don’t need it. In practice, I have found your CODEBASE parameter must have an absolute http://
-style reference to the base directory where the code is stored. The codebase is only needed when your code resides somewhere other than where the html page was loaded from.
For a local hard disk, the only thing I could get to work on NT with all browsers and Appletviewers is leaving the CODEBASE out entirely which causes the CODEBASE to default
to the same directory as where the enclosing HTML page was loaded from. You may find for your platform you have to code it something like this: file:///C|//MyDir/
or C:\MyDir\. I also further suspect that some browsers will take the a relative CODEBASE as relative to each element of the CLASSPATH, not relative
to the current HTML directory. If the user of the signed Applet is behind a firewall, for some strange reason, if he invokes the Applet
using the IP rather than the DNS name of the website in the codebase e.g CODEBASE= "http://65.110.21.43/"
instead of CODEBASE= "mindprod.com" , all works. Otherwise you get a trustProxy Property
error message. |
| vspace= "10" |
pixel width of border above and below the Applet |
| hspace= "10" |
pixel width of border left and right of the Applet |
| align= "left" |
how this Applet aligns, treated like a image |
| alt= "You need Java to run this Applet" |
what to display if no Java interpreter available. Normally this would be the same text that appears just before the </applet> tag. This
optional attribute specifies any text that should be displayed if the browser understands the APPLET tag but can’t run Java Applets. |
| name= "receiver" |
Name for this Applet so that other Applets can communicate with it. Other Applets would do
a Applet Applet.getAppletContext(). getApplet( "receiver"
) to get a handle on this Applet. You don’t need this parameter if you use Applet Enumeration Applet.
getAppletContext(). getApplets() which gets you a list of all the Applets running on
the page (including yourself). |
| mayscript |
Lets Applet read/write cookies and peek at the page it is embedded in using JavaScript DOM. |
| > |
All that stuff above has to be inside the <applet… >, but the params may not be. |
| <param name= "favouriteColour" value= "orange" > |
The param statements are Java’s ode to verbosity. They pass information to the Applet. There can be as many
param statements as you like. Beware of params with decimal points. <param name= "cost" value="10.00"
> When your Applet runs in Europe, it may be expecting a comma instead unless you take special precautions.
Param values cannot contain embedded " or newline characters. You can encode the parameters using HTML entities such as ",
> or &#nn;. The browser should automatically convert them for you to the equivalent character when you do
your getParam. If the browser does not convert them for you, you can convert the entities back to characters with my free entities
package. I tested recent versions of Opera, Netscape, Firefox, Mozilla and IE and they call converted entities to characters automatically. Unfortunately, there is no &
entity for \n. and 
 do not work. You will have to roll your own
convention, perhaps using the character pair \n or some rarely used character such as ~ or ` to
stand in for newline. You can’t use <br> because < and > are awkward
characters in their own right. Awkward characters are defined as ones that have be specially escaped/quoted/represented to use them literally because
they have special meaning as commands/delimiters. This encoding is natural. Fussing with entities only kicks in when you have awkward characters. Further, the way you encode
parameters is completely familiar — almost the same way you encode awkward characters in HTML body text. Watch out for &#xnnnn; and &#nnnn;
style entities. What they mean depends on the enclosing HTML document encoding.
Alternatively, you could write a little utility to use java.net. URLEncoder to encode the string, then manually include
it as the param value, then use java.net. URLDecoder inside the Applet to make sense of the
parameter. URLEncoder encodes space as + and special characters as %xx hex, so you can do the
encoding in your head once you see a few examples. The catch is, once you hook up URLDecoder to a param, you can’t use that param anymore for
plain text, at least not completely transparently.
If you wanted to disguise the value, you could encode it with base64 or base64u armouring.
Applet parameter names are case insensitive (Case does not matter. Names can be upper or lower case). Applet parameter values are case sensitive (passed
exactly as written to your Applet’s getParameter. If you want lower case, use parmValue.) toLowerCase(). |
| <img src= "image/NoJava4U.jpg" > |
image to display if no Java interpreter available. |
| You need Java to run this Applet |
Text that will display on a really stupid browser that has no idea what an Applet tag is. |
| </applet> |
and finally the ending tag for the |
A minimal Applet invocation might look like this:
<applet code="MyApplet.class" width="330" height="240">
</applet>
Make sure you get your < ’s and > ’s in the right places.
A more typical Applet invocation might look like this:
<applet
archive="../mypackage.jar"
code="com.mindprod.mypackage.MyClass.class"
width="565" height="46"
alt="Java needed to display this Applet.">
<param name="flavour" value="strawberry">
Java needed to display this Applet.
</applet>
To run Applets in Internet Explorer 5.5 or Netscape 4.79 with the old Java 1.3 Plugin before the courts smacked Microsoft for their violation of
their agreement with Sun, you need a hideously complicated syntax using nested <OBJECT> and <EMBED>tags.
The best way to generate them is to use the HTML converter program on your simple <applet tags. You don’t need them to run with the Plug-in
1.4 in the recent versions of Opera, Mozilla, Firefox, Netscape and IE. Further, the latest Mozilla can’t even understand them. Their only advantage is they can arrange
to install a Java JRE if one is not installed already. I boycott them on the grounds of terminal ugliness.
<applet, from a CSS point of view, is just another tag. In your CSS style sheet, you can apply properties to it, adjust the margin spacing, put
borders around it… In your HTML markup you can give it a class or id. Unfortunately Mozilla, Netscape and Firefox all have a common bug and don’t display a border
around Applets even when you ask them to. Opera and IE work properly.
<OBJECT> and <EMBED>
In theory, <applet has been deprecated and you should use the more generic, verbose, error-prone <OBJECT tag. <OBJECT
has some minor nice features, like a standby message and a way of providing alternate implementations if the user’s browser does not support Java. It can work with
serialised Applets. It works for languages and plug-ins other than Java. However, <OBJECT is still not as widely
supported as <applet, so it is probably wiser to stick with <applet. See the HTML
spec for details.
Starting with JDK 1.4.2, you can arranged that jars be cached at the client site using the EMBED tag cache_archive
parameter.
That was the polite version, but here is what I really think of <OBJECT> and <OBJECT> tags. Anti-Java,
rather corrupt people launched a successful attempt to derail Java by somehow convincing some weak minded folk at the W3C to deprecate the <applet
tags. Browser makers have all sensibly resisted this foul play and all continue to support <applet. The replacement is an utterly preposterous
and verbose scheme using <OBJECT> and <OBJECT> tags that works in different ways in different browsers.
The scheme is beyond ridiculous. It is so baroque, you can’t even hand code it. You have to use an automated tool to convert <applet tags
into pages and pages of gobbledegook. Don’t use them! If you ignore my advice, you might as well add to the flakiness by using the Java
Deployment Toolkit to generate the tags with JavaScript.
Tell the W3C and Microsoft to shove their <OBJECT> and <EMBED> and lunatic classids
to a foul-smelling place. Please, do not use these tags!
You can use a simple 
Jump
to Java Button to handle a missing JRE.
Switch Hitter: Applet ⇒ application
By adding the following method to your Applet, you can allow it be run either as an Applet or as an application. I call
these dual mode programs hybrids or switch hitters. If your Applet were called MyApplet, here is
the code to add to the MyApplet class to make it also into an application:
Your Applet can get hold of the parameters in the HTML.
That code is quite crude. It will not do such things as:
- Simulate the getParameter method to get at the Applet parameters.
- Adjust the co-ordinate system so part of the Applet is not hidden under the Frame menu bar. Layout managers deal with
this automatically, but if you do absolute positioning, you have to compensate manually..
- It does not simulate getAppletContext. Code defensively to deal with a null return.
The easiest way to deal with these problems is to use two Applet constructors, one the usual default constructor and one that passes the param
information in. Inside you can keep track of which mode you are running in with a boolean you set in the constructor. getParameter(
"favouriteColour" ) will return the String "orange" . When you write an Applet
often you will override some of the following methods: init(), start() , stop() , destroy()
and paint(Graphics g).
There is equivalent code for JApplet.
Switch Hitter: application ⇒ Applet
What if you already have an application? how to you allow it to run also as an Applet? An Applet is just a Panel
with init, start, stop and destroy methods. Write an Applet
shell that does a this.add to add your application into the Applet in its init method, just
as you would any other Panel.
Transparency
Though it is possible to create transparent and translucent components using colours with the alpha channel ( the fourth number in new
Color ( red, green, blue, alpha )) set to
something other than 0xff, I have found no way to make the Applet or JApplet itself transparent.
You could pass the colour of the web page’s background in as an Applet param or have JavaScript communicate that information to Java. This
would only give true transparency only when the browser were using a plain untextured background.
Loading A Web Page
Often you want to display some other web page. You can trick the browser into doing that for you with:
this.getAppletContext().showDocument( url, window );
Your Applet does not get to see the web page. It goes straight to the browser for rendering. Because this feature can be so easily abused to
wallpaper the user’s screen with popups, it is now often blocked.
InterApplet Communication
Communication between Applets running on the same page, it turns out, is much simpler than you might imagine. First, there is only one
program per web page running. In fact there is only one program per browser running. Applets are just a bunch of ordinary objects. Applets
from the same class share the same static variables! Objects can call each other’s methods. They are all in the same address space. There is thus almost zero problem
with interApplet communications. Your only problem is finding the other Applet objects on your page to talk to. There are two mechanisms for that,
- Applet Applet. getAppletContext(). getApplet( "receiver"
)
that accesses another Applet uniquely identified via a name you assign in the HTML <applet name= tag.
- Applet Enumeration Applet.getAppletContext().getApplets()
that gets you a list of all the Applets, of any class, not just yours, running on the page (including yourself).
An Applet propagates information around by putting it in static variables, or by passing parameters to the methods of other objects to get them to
do something with the information. There is only one thread, not one per Applet. You can’t just deposit information and expect the other Applets
to notice the change.
The browser may decide to kill (forget) Applets not on the current page, and then again it may not. Presumably, if you held onto a reference to
offscreen Applets in your onscreen Applet, or in a common doubly linked object, those offscreen objects would have
to stay alive.
Applet Classpath
Applets use the ordinary local classpath. This can cause trouble since the developer’s classpath and the end user’s classpath won’t
usually match. There are two sorts of trouble that ensue:
- If you have any classes not in a package, these non-uniquely named classes could conflict with ones on the end-user’s local hard disk. To avoid this problem, put any
classes ever used by Applets in some globally uniquely named package, e.g. com.mindprod.business
- You, as developer, may forget to include a necessary class in your jar, usually from some peripheral package. It will work fine on your machine, but will fail on the customer’s
machine. On your machine, the JVM finds the missing class via the classpath. On the end user’s machine that search fails.
- You as developer may test an Applet jar, yet actually may be using some fresher classes on your local hard disk. You inadvertently ship stale code.
On the other paw, the Applet classpath can work in the developer’s favour. If an Applet requires a huge support
class library, he can ask the user to download and install it on his local hard disk and point the classpath to it (or put it in the ext directory). Then the class library
will be immediately available every time the Applet runs.
Applet vs Application
When you are starting a project, which should it be, an Applet or application or both? The advantages of using an Applet
are:
- You can get the browser to render HTML for you.
- You can direct the browser to fetch and display material off the web.
- The user automatically gets the latest version of the software.
- There is nothing to install.
The disadvantages of using an Applet are:
- To do anything interesting, you must use signed Applets. There are many different signing schemes to support. Signing is complicated.
- Applets must co-exist with a browser. There is less RAM available to work.
- Applets must co-exist with a variety of browsers and their variety of bugs and lack of support. IE supports only Java 1.14 with no RMI, Swing,
Collections etc. It is almost impossible to write code that dodges all the bugs in all the browsers.
- Applets must be loaded over the Internet afresh each time. This can be time consuming for fat ones. Modern browsers now cache Applets,
so this is no longer a disadvantage.
- Web Start is designed to distribute and update applications, not Applets.
- To start an Applet, you must first start a browser.
- You can’t use native code compilers on Applets, only applications. This means your speed will be limited to the JVM supported by the browser.
- You may not be able to force the user to update the browser to something recent.
There is a third possibility that has some of the advantage of both Applet and application called Java Web Start.
Applet vs Servlet
The current fashion is to use Servlets exclusively for all web based applications. I think this is idiotic. It has made data entry even more
primitive than it was on the keypunch. The advantages of using Applets over Servlets are:
- With Applets, the user can find out about keying errors right away, not with cryptic messages that appear only after you hit submit
and wait several seconds.
- With Applets, data entry can be much more sophisticated, with keystroke validation, code lookup, pattern validation, bounds checking, mandatory
field validation, prompting, help etc.
- With Applets, data communications can go on in the background and can be cached or procrastinated giving the illusion of instant response.
- With Applets, you don’t have to fill in a giant form only to discover the server won’t accept it.
- With Applets, you can run your applications on a cheap vanilla HTML server. You don’t need a complex, expensive to maintain, Servlet
womb.
- With Applets, you don’t have to resort to dog’s breakfast kludges like Ajax to provide even tiny bits of client
side intelligence.
- With Applets, you have have sufficient local intelligence to send much terser binary compressed messages back and forth with the server. You can
also exchange serialised Object trees.
The disadvantages of using Applets over Servlets are:
- With Applets, a recent Java must be properly installed at the client. This is more difficult to arrange than you might imagine especially with the
FUD from Sun’s competitors spreading misinformation about the danger of using Java when actually it is the safest language going.
- With Applets, you can’t use low cost web designers to help create your applications. With Servlets and a framework
markup language the designers don’t have to write Java code, just HTML, peppered with a bit of gibberish.
- With Applets that connect with a database, you need a mixture of client size and server side code. This requires two sets of skills, and keeping
server and client size code in sync.
- Applets that do almost anything interesting have to be digitally signed. This is an annoyance to users and frightens them off.
Splash Logo
In Java 1.5+ there is a splash logo that comes up as your Applet loads. It sort of a radiant Sun-like image. You can modify that with a magic <param
tag that provides an alternate scalable image.
Applet Sound
Applets can play *.au files, (and *.wav files in Windows) this way:
Runtime Parameters
You can control the browser’s JVM runtime parameters (see java.exe) that control stack and heap sizes etc. from the Java Control Panel. click
Start ⇒ Control Panel ⇒ Java ⇒ Java ⇒ Java Applet Settings ⇒ View . Add the required parameters in the 4th column, next to the JVM. It does not
look like it is editable, but it is.
Learning More
Sun’s Javadoc on the
Applet class : available:
Sun’s JDK Technote Guide on
Applet Caching : available:
2008-03-14 by Roedy Green ©1996-2009 Canadian Mind Products
Please email your feedback for publication, errors, omissions, broken/redirected link reports
