Properly resolve referenced forms.

src/htmx.js

@@ -3523,7 +3523,7 @@ var htmx = (function() {
 
     // for a non-GET include the closest form
     if (verb !== 'get') {
-      processInputValue(processed, priorityFormData, errors, closest(elt, 'form'), validate)
+      processInputValue(processed, priorityFormData, errors, ('form' in elt && elt.form) || closest(elt, 'form'), validate)
     }
 
     // include the element itself

test/core/ajax.js

@@ -1184,6 +1184,48 @@ describe('Core htmx AJAX Tests', function() {
     values.should.deep.equal({ t1: 'textValue', b1: ['inputValue', 'buttonValue'] })
   })
 
+  it('sends referenced form values when a button referencing another form is clicked', function() {
+    var values
+    this.server.respondWith('POST', '/test3', function(xhr) {
+      values = getParameters(xhr)
+      xhr.respond(205, {}, '')
+    })
+
+    make('<form id="externalForm" hx-post="/test">' +
+            '<input type="text" name="t1" value="textValue">' +
+            '<input type="hidden" name="b1" value="inputValue">' +
+            '</form>' +
+            '<form hx-post="/test2">' +
+            '<input type="text" name="t1" value="checkValue">' +
+            '<button id="submit" form="externalForm" hx-post="/test3" type="submit" name="b1" value="buttonValue">button</button>' +
+            '</form>')
+
+    byId('submit').click()
+    this.server.respond()
+    values.should.deep.equal({ t1: 'textValue', b1: ['inputValue', 'buttonValue'] })
+  })
+
+  it('sends referenced form values when a submit input referencing another form is clicked', function() {
+    var values
+    this.server.respondWith('POST', '/test3', function(xhr) {
+      values = getParameters(xhr)
+      xhr.respond(204, {}, '')
+    })
+
+    make('<form id="externalForm" hx-post="/test">' +
+            '<input type="text" name="t1" value="textValue">' +
+            '<input type="hidden" name="b1" value="inputValue">' +
+            '</form>' +
+            '<form hx-post="/test2">' +
+            '<input type="text" name="t1" value="checkValue">' +
+            '<input id="submit" form="externalForm" hx-post="/test3" type="submit" name="b1" value="buttonValue">' +
+            '</form>')
+
+    byId('submit').click()
+    this.server.respond()
+    values.should.deep.equal({ t1: 'textValue', b1: ['inputValue', 'buttonValue'] })
+  })
+
   it('properly handles inputs external to form', function() {
     var values
     this.server.respondWith('Post', '/test', function(xhr) {

www/content/docs.md

@@ -640,8 +640,8 @@ will include the values of all inputs within it.
 
 As with HTML forms, the `name` attribute of the input is used as the parameter name in the request that htmx sends.
 
-Additionally, if the element causes a non-`GET` request, the values of all the inputs of the nearest enclosing form
-will be included.
+Additionally, if the element causes a non-`GET` request, the values of all the inputs of the associated form will be
+included (typically this is the nearest enclosing form, but could be different if e.g. `<button form="associated-form">` is used).
 
 If you wish to include the values of other elements, you can use the [hx-include](@/attributes/hx-include.md) attribute
 with a CSS selector of all the elements whose values you want to include in the request.