<apex:page standardController="Account">
<apex:form>
<apex:outputPanel id="panel1">
 <apex:commandLink rerender="panel1" value="Update panel1" />
 <table><tr>
 <apex:repeat value="{!account.Contacts}" var="act">
  <apex:outputPanel>
  <td>Bob - {!NOW()}</td>
  </apex:outputPanel>
 </apex:repeat>
 </tr></table>
</apex:outputPanel>

<apex:outputPanel id="panel2">
 <apex:commandLink rerender="panel2" value="Update panel2" />
 <table><tr>
 <apex:repeat value="{!account.Contacts}" var="act">
  <td>Fred - {!NOW() }</td>
 </apex:repeat>
 </tr></table>
</apex:outputPanel>
</apex:form>
</apex:page>

Contact c = new Contact();
Database.SaveResult result = Database.insert(c, false);

// Have multiple rules requiring fields to be set
System.debug('Num errors: ' + result.getErrors().size());  // Returns 1

boolean success = false;

Savepoint sp = Database.setSavepoint();
try
{
    insert obj;
    success = true;
}
catch (DmlException ex)
{
    ... render and process errors ...
}
Database.rollback(sp);

<apex:page controller="bookingWizController">
  <apex:sectionHeader title="Confirm Flight Booking" subtitle="Step 0 of 7"/>
    <apex:form >
      <apex:pageBlock title="Define Flight Name" mode="edit">
        <apex:pageBlockButtons >
            <apex:commandButton action="{!step1}" value="Next"/>
        </apex:pageBlockButtons>
        <apex:pageBlockSection title="Test set Flight">
            <apex:outputField id="flight" value="{!flight.name}"/>
        </apex:pageBlockSection>
        <apex:pageBlockSection title="Test pick account">
            <apex:inputField id="account" value="{!flight.Flight_Account__c}" required="true"/>
        </apex:pageBlockSection>        
        <apex:pageBlockSection title="Test pick dep airport">
            <apex:inputField id="dep_airport" value="{!flight.Flight_departure_airport__c}" required="true"/>
        </apex:pageBlockSection>     
        <apex:pageBlockSection title="Test pick arr airport">
            <apex:inputField id="arr_airport" value="{!flight.Flight_arrivals_airport__c}" required="true"/>
        </apex:pageBlockSection>
    </apex:pageBlock>
  </apex:form>
</apex:page>

<apex:dataTable columns="2" value="{!AllLicenseFeatures}" var="feature">
  <apex:column>
    <apex:facet name="header">Available Features</apex:facet>
    <apex:inputCheckbox value="{!feature.name}" id="feature{!feature.name}" onChange="toggle('feature{!feature.name}Expiration')" />
  </apex:column>
  <apex:column>
    <apex:facet name="header">Expiration Date</apex:facet>
    <apex:InputField id="feature{!feature.name}Expiration" value="{!feature.Expiration_Date__c}" />
  </apex:column>
</apex:dataTable>

List<String> feature_names = new List<String>{'Feature A','Feature B','Feature C'};
License_Feature__c[] features = new License_Feature__c[feature_names.size()];

public License_Feature__c getLicenseFeature(Integer i){
   if (features[i] == null) features[i] = new License_Feature__c();
   return features[i];
}
public License_Feature__c[] getAllLicenseFeatures() {
   integer i;
   for ( i = 0; i < feature_names.size() ; i ++) {
       features[i] = getLicenseFeature(i);
       features[i].name = feature_names[i];
   }
   return features;
}

public class TabTest {


 public String ActiveTab {get; set;} 
 
 
 public TabTest() {
  this.ActiveTab = 'Tab2'; 
 }


}

<apex:page controller="conLeadTab" action="{!validate}">
<apex:pageBlock id="mypageblock" mode="new">
                 <apex:param id="vesg"   name="vesg" value=""/>
     </apex:pageBlock>
<script language="javascript">
var vesgval = 'SOme value';
//The line below does not work, but here I need to assign the value of vesgval to the parameter vesg
//{!$CurrentPage.parameters.vesg}=vesgval;
</script>  
</apex:page> 

  public PageReference validate() {
      this.pesgval = System.currentPageReference().getParameters().get('vesg');
      System.debug('this.pesgval--->>>'+this.pesgval);
               if(pesgval==null || pesgval.length()==0){
                    PageReference secondPage1 = new PageReference('/apex/editLeadError');
                        secondPage1.setRedirect(true);
                  return secondPage1; 
                  
                 } else{//do something else, but the execution never comes here as the value of pesgval is always NULL}          
            return null;      
                }

<apex:repeat value="{!Test}" var="t">
 <apex:outputpanel layout="block" rendered="{IF(t.val,true,false)}">
      <tr>
   <td colspan="2" >
    {!t.Name}
   </td>
  </tr>
 </apex:outputpanel>
</apex:repeat>