When the value attribute is omitted, the progress element becomes indeterminate, that is, it shows activity but not how much progress has actually been made. If the value attribute is used without a max value, the range is from 0 to 1. The following example shows the effect of value on an HTMLProgressElement.
- HTML5 A vocabulary and associated APIs for HTML and XHTML, Section 4.10.16
Microsoft Developer Network: [Windows Internet Explorer API reference Article]