function EstaVacia(Cadena)
{     
	 if (Cadena == "" || Cadena == null)
	 {
		return true
	 }
	 else  
		return (!TieneLetras(Cadena))
}
  

function TieneLetras(Cadena)
{  
	 var i=0;
	 var Largo=Cadena.length

	 while(Cadena.charAt(i)==' ' && i<Largo)         
		i++
	 
	 if (i == Cadena.length)
		return false;
	 else
		return true;
}

function emailCheck (emailStr) 
{
	/* The following pattern is used to check if the entered e-mail address
	   fits the user@domain format.  It also is used to separate the username
	   from the domain. */
	var emailPat=/^(.+)@(.+)$/
	/* The following string represents the pattern for matching all special
	   characters.  We don't want to allow special characters in the address.
	   These characters include ( ) < > @ , ; : \ " . [ ]    */
	var specialChars="\\(\\)<>@,;:\\\\\\\"\\.\\[\\]"
	/* The following string represents the range of characters allowed in a
	   username or domainname.  It really states which chars aren't allowed. */
	var validChars="\[^\\s" + specialChars + "\]"
	/* The following pattern applies if the "user" is a quoted string (in
	   which case, there are no rules about which characters are allowed
	   and which aren't; anything goes).  E.g. "jiminy cricket"@disney.com
	   is a legal e-mail address. */
	var quotedUser="(\"[^\"]*\")"
	/* The following pattern applies for domains that are IP addresses,
	   rather than symbolic names.  E.g. joe@[123.124.233.4] is a legal
	   e-mail address. NOTE: The square brackets are required. */
	var ipDomainPat=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/
	/* The following string represents an atom (basically a series of
	   non-special characters.) */
	var atom=validChars + '+'
	/* The following string represents one word in the typical username.
	   For example, in john.doe@somewhere.com, john and doe are words.
	   Basically, a word is either an atom or quoted string. */
	var word="(" + atom + "|" + quotedUser + ")"
	// The following pattern describes the structure of the user
	var userPat=new RegExp("^" + word + "(\\." + word + ")*$")
	/* The following pattern describes the structure of a normal symbolic
	   domain, as opposed to ipDomainPat, shown above. */
	var domainPat=new RegExp("^" + atom + "(\\." + atom +")*$")
	
	
	/* Finally, let's start trying to figure out if the supplied address is
	   valid. */
	
	/* Begin with the coarse pattern to simply break up user@domain into
	   different pieces that are easy to analyze. */
	var matchArray = emailStr.match(emailPat)
	if (matchArray==null) {
	  /* Too many/few @'s or something; basically, this address doesn't
		 even fit the general mould of a valid e-mail address. */
		alert("La entrada de correo parece ser incorrecta")
		return false
	}
	var user=matchArray[1]
	var domain=matchArray[2]
	
	// See if "user" is valid
	if (user.match(userPat)==null) {
		// user is not valid
		alert("El nombre de usuario parace no ser correcto.")
		return false
	}
	
	/* if the e-mail address is at an IP address (as opposed to a symbolic
	   host name) make sure the IP address is valid. */
	var IPArray=domain.match(ipDomainPat)
	if (IPArray!=null) {
		// this is an IP address
		  for (var i=1;i<=4;i++) {
			if (IPArray[i]>255) {
				alert("Direccion IP no valida!")
			return false
			}
		}
		return true
	}
	
	// Domain is symbolic name
	var domainArray=domain.match(domainPat)
	if (domainArray==null) {
		alert("El nombre de dominio parace no ser correcto.")
		return false
	}
	
	/* domain name seems valid, but now make sure that it ends in a
	   three-letter word (like com, edu, gov) or a two-letter word,
	   representing country (uk, nl), and that there's a hostname preceding
	   the domain or country. */
	
	/* Now we need to break up the domain to get a count of how many atoms
	   it consists of. */
	var atomPat=new RegExp(atom,"g")
	var domArr=domain.match(atomPat)
	var len=domArr.length
	if (domArr[domArr.length-1].length<2 ||
		domArr[domArr.length-1].length>3) {
	   // the address must end in a two letter or three letter word.
	   alert("La direccion de correo debe acabar en 3 letras de dominio o 2 de un pais.")
	   return false
	}
	
	
	  if ((emailStr.indexOf(".gob")<5)&&(emailStr.indexOf(".com")<5)&&(emailStr.indexOf(".org")<5)
	  &&(emailStr.indexOf(".gov")<5)&&(emailStr.indexOf(".net")<5)
	  &&(emailStr.indexOf(".mil")<5)&&(emailStr.indexOf(".edu")<5)){
	   alert("La direccion correo es valida."
	   +" La direccion correo debe contener un sufijo del tipo "
	   +".com,.gob,.net,.org,.gov,.edu o .mil");
	   return false
	  }
	
	// Make sure there's a host name preceding the domain.
	if (len<2) {
	   var errStr="Esta direccion es desconocida como IP!"
	   alert(errStr)
	   return false
	}
	
	// If we've gotten this far, everything's valid!
	<!-- alert('La direccion de e-mail introducida parace correcta. Gracias');
	return true;
}