WML is designed to meet the constraints of a wide range of small, narrowband devices. These devices are primarily characterized in four ways:
Display size--smaller screen size and resolution. A small mobile device such as a phone may only have a few lines of textual display, each line containing 8-12 characters.
Input devices--a limited, or special-purpose input device. A phone typically has a numeric keypad and a few additional function-specific keys. A more sophisticated device may have software-programmable buttons, but may not have a mouse or other pointing device.
Computational resources--low power CPU and small memory size, often limited by power constraints.
Narrowband network connectivity--low bandwidth and high latency. Devices with 300bps to 10kbps network connections and 5-10 second round-trip latency are not uncommon.
This document uses the following terms to define broad classes of device functionality:
Phone--the typical display size ranges from two to ten lines. Input is usually accomplished with a combination of a numeric keypad and a few additional function keys. Computational resources and network throughput are typically limited, especially when compared with more general-purpose computer equipment.
PDA--a Personal Digital Assistant is a device with a broader range of capabilities. When used in this document, it specifically refers to devices with additional display and input characteristics. A PDA display often supports resolution in the range of 160x100 pixels. A PDA may support a pointing device, handwriting recognition, and a variety of other advanced features.
These terms are meant to define very broad descriptive guidelines and to clarify certain examples in the document.