A button that is rendered as an HTML input element with the type attribute set to submit, reset, or image, depending on the <apex:commandButton> tag's specified values.
The button executes an action defined by a controller, and then either refreshes the current page, or navigates to a different page based on the PageReference variable that is returned by the action.
An <apex:commandButton> component must always be a child of an <apex:form> component.
See also: <apex:commandLink>
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A. B. C. D.A.
The correct answer to the question is A. apex:commandButton.
An apex:commandButton tag is used to create a button on a Visualforce page that performs an action when clicked. The button is rendered as an HTML input element with the type attribute set to submit, reset, or image, depending on the tag's specified values.
When the button is clicked, it executes an action defined by a controller. The action can perform any number of operations, such as updating records, running queries, or performing calculations. Once the action is complete, the page can be refreshed or navigated to a different page based on the PageReference variable that is returned by the action.
One important thing to note is that an apex:commandButton component must always be a child of an apex:form component. This is because the button's action is defined by the controller, and the controller requires access to the data in the form to perform its operations. By placing the button inside a form, the controller can access this data and perform the necessary actions.
Other Visualforce components that are related to apex:commandButton include apex:commandLink, which creates a link that performs an action when clicked, and apex:actionRegion, which defines a section of the page that can be refreshed independently of the rest of the page.
In summary, apex:commandButton is a Visualforce component that creates a button on a page that performs an action when clicked. The button is rendered as an HTML input element and must always be placed inside an apex:form component.