From http://www.w3schools.com (Copyright Refsnes Data)

HTML 5 <dialog> tag

Definition and Usage

The <dialog> tag defines a dialog, such as a conversation.

Differences Between HTML 4.01 and HTML 5

The <dialog> tag is new in HTML 5

Tips and Notes

Note: Every sentence in dialog must belong to a part, defined with the <dt> tag. See the example below.

Example

Source	Output
<dialog> <dt>Teacher</dt> <dd>What is 2+2</dd> <dt>Student</dt> <dd>4</dd> <dt>Teacher</dt> <dd>Correct!</dd> </dialog>	Teacher What is 2+2 Student 4 Teacher Correct!

Standard Attributes

class, contenteditable, contextmenu, dir, draggable, id, irrelevant, lang, ref, registrationmark, tabindex, template, title

For a full description, go to Standard Attributes in HTML 5.

Event Attributes

onabort, onbeforeunload, onblur, onchange, onclick, oncontextmenu, ondblclick, ondrag, ondragend, ondragenter, ondragleave, ondragover, ondragstart, ondrop, onerror, onfocus, onkeydown, onkeypress, onkeyup, onload, onmessage, onmousedown, onmousemove, onmouseover, onmouseout, onmouseup, onmousewheel, onresize, onscroll, onselect, onsubmit, onunload

For a full description, go to Event Attributes in HTML 5.