Evolution of mobile web standards
The Handheld Device Markup Language (HDML) is a markup language  intended for display on handheld computers, information appliances, smartphones, etc.. It is similar to HTML, but for wireless and handheld devices with small displays, like PDA, mobile phones and so on.
It was originally developed in about 1996 by Unwired Planet, the company that became Phone.com and then Openwave. HDML was submitted to W3C for standardization, but was not turned into a standard. Instead it became an important influence on the development and standardization of WML, which then replaced HDML in practice. (Although HDML is still in use in Japan by KDDI brands such as au, especially for mobile banking solutions.)
See also