Added warnings regarding duplicate files to <zip> and family.

PR: 30339


git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@277071 13f79535-47bb-0310-9956-ffa450edef68

docs/manual/CoreTasks/ear.html

@@ -16,6 +16,12 @@ The same thing can be accomplished by using the <i>prefix</i> and <i>fullpath</i
 attributes of zipfilesets in a Zip or Jar task.)</p>
 <p>The extended zipfileset element from the zip task (with attributes <i>prefix</i>, <i>fullpath</i>, and <i>src</i>) is available in the Ear task.</p>
 
+<p><b>Please note that the zip format allows multiple files of the same
+fully-qualified name to exist within a single archive.  This has been
+documented as causing various problems for unsuspecting users.  If you wish
+to avoid this behavior you must set the <code>duplicate</code> attribute
+to a value other than its default, <code>&quot;add&quot;</code>.</b></p>
+
 <h3>Parameters</h3>
 <table border="1" cellpadding="2" cellspacing="0">
   <tr>

docs/manual/CoreTasks/jar.html

@@ -54,6 +54,12 @@ Note in particular that this may result in manifest lines greater than 72 bytes
 being wrapped and continued on the next line.
 </p>
 
+<p><b>Please note that the zip format allows multiple files of the same
+fully-qualified name to exist within a single archive.  This has been
+documented as causing various problems for unsuspecting users.  If you wish
+to avoid this behavior you must set the <code>duplicate</code> attribute
+to a value other than its default, <code>&quot;add&quot;</code>.</b></p>
+
 <h3>Parameters</h3>
 <table border="1" cellpadding="2" cellspacing="0">
   <tr>

docs/manual/CoreTasks/war.html

@@ -18,6 +18,12 @@ The same thing can be accomplished by using the <i>prefix</i> and <i>fullpath</i
 attributes of zipfilesets in a Zip or Jar task.)</p>
 <p>The extended zipfileset element from the zip task (with attributes <i>prefix</i>, <i>fullpath</i>, and <i>src</i>) is available in the War task.</p>
 
+<p><b>Please note that the zip format allows multiple files of the same
+fully-qualified name to exist within a single archive.  This has been
+documented as causing various problems for unsuspecting users.  If you wish
+to avoid this behavior you must set the <code>duplicate</code> attribute
+to a value other than its default, <code>&quot;add&quot;</code>.</b></p>
+
 <h3>Parameters</h3>
 <table border="1" cellpadding="2" cellspacing="0">
   <tr>

docs/manual/CoreTasks/zip.html

@@ -67,6 +67,12 @@ Ant uses the algorithm used by <a href="http://www.info-zip.org">Info-Zip's</a>
 implementation of the zip and unzip commands - these are the default
 versions of zip and unzip for many Unix and Unix-like systems.</p>
 
+<p><b>Please note that the zip format allows multiple files of the same
+fully-qualified name to exist within a single archive.  This has been
+documented as causing various problems for unsuspecting users.  If you wish
+to avoid this behavior you must set the <code>duplicate</code> attribute
+to a value other than its default, <code>&quot;add&quot;</code>.</b></p>
+
 <h3>Parameters</h3>
 <table border="1" cellpadding="2" cellspacing="0">
   <tr>