<input type="image"> - HTML: Hypertext Markup Language
supported common attributes alt, src, width, height, formaction, formenctype, formmethod, formnovalidate, formtarget idl attributes none.
... alternate string to display when the image can't be shown formaction the url to which to submit the data formenctype the encoding method to use when submitting the form data formmethod the http method to use when submitting the form formnovalidate a boolean which, if present, indicates that the form shouldn't be validated before submission formtarget a string indicating a browsing context from where to load the results of submitting the form height the height, in css pixels, at which to draw the image src the url from which to load the image width the width, in css pixels, at which to draw the image alt the alt attribute provides an alternate string to use as the button's label if the image canno...
... formtarget a string which specifies a name or keyword that indicates where to display the response received after submitting the form.
... formtarget html5 a name or keyword indicating where to display the response that is received after submitting the form.

HTMLButtonElement - Web APIs
htmlbuttonelement.formtarget is a domstring reflecting a name or keyword indicating where to display the response that is received after submitting the form.
... the following attributes have been added: autofocus, formaction, formenctype, formmethod, formnovalidate, formtarget, labels, validity, validationmessage, and willvalidate.

HTMLInputElement - Web APIs
formtarget string: returns / sets the element's formtarget attribute, containing a name or keyword indicating where to display the response that is received after submitting the form.
... the following properties have been added: autocomplete, autofocus, dirname, files, formaction, formenctype, formmethod, formnovalidate, formtarget, height, indeterminate, labels, list, max, min, multiple, pattern, placeholder, required, selectiondirection, selectionend, selectionstart, step, validationmessage, validity, valueasdate, valueasnumber, width, and willvalidate.

<input type="submit"> - HTML: Hypertext Markup Language
formnovalidate a boolean which, if present, means the form's fields will not be subjected to constraint validation before submitting the data to the server formtarget the browsing context into which to load the response returned by the server after submitting the form formaction a string indicating the url to which to submit the data.
... formtarget a string which specifies a name or keyword that indicates where to display the response received after submitting the form.

<input>: The Input (Form Input) element - HTML: Hypertext Markup Language
all associates the control with a form element formaction image, submit url to use for form submission formenctype image, submit form data set encoding type to use for form submission formmethod image, submit http method to use for form submission formnovalidate image, submit bypass form control validation for form submission formtarget image, submit browsing context for form submission height image same as height attribute for <img>; vertical dimension list almost all value of the id attribute of the <datalist> of autocomplete options max numeric types maximum value maxlength password, search, tel, text, url maximum length (number of characters) of value ...
... formtarget valid for the image and submit input types only.

HTML attribute reference - HTML: Hypertext Markup Language
formtarget <button>, <input> if the button/input is a submit button (type="submit"), this attribute specifies the browsing context (for example, tab, window, or inline frame) in which to display the response that is received after submitting the form.

<button>: The Button element - HTML: Hypertext Markup Language
formtarget html5 if the button is a submit button, this attribute is a author-defined name or standardized, underscore-prefixed keyword indicating where to display the response from submitting the form.

<form> - HTML: Hypertext Markup Language
this value can be overridden by a formtarget attribute on a <button>, <input type="submit">, or <input type="image"> element.

<iframe>: The Inline Frame element - HTML: Hypertext Markup Language
this can be used in the target attribute of the <a>, <form>, or <base> elements; the formtarget attribute of the <input> or <button> elements; or the windowname parameter in the window.open() method.

<input type="range"> - HTML: Hypertext Markup Language
note: the following input attributes do not apply to the input range: accept, alt, checked, dirname, formaction, formenctype, formmethod, formnovalidate, formtarget, height, maxlength, minlength, multiple, pattern, placeholder, readonly, required, size, src, and width.