is broader and focuses on the environmental constraints and opportunities for behavior, as in Gibsonian ecological psychology and ecological interface design (Vicente, 1999; Bennett & Flach, 2011, p. 61) Documentation Since the 1980s, a major change in technical documentation has been to emphasize the tasks performed with a system rather than documenting the system itself. In software documentation particularly, long printed technical manuals that exhaustively describe every function of the software are being replaced by online help organized into tasks. This is part of the new emphasis on usability and user-centered design rather than system/software/product design. This task orientation in technical documentation began with publishing guidelines issued by IBM in the late 1980s. Later IBM studies led to John Carroll's theory of minimalism in the 1990s. With the development of XML as a markup language suitable for both print and online documentation (replacing SGML with its focus on print), IBM developed the Darwin Information Typing Architecture XML standard in 2000. Now an OASIS standard, DITA has a strong emphasis on task analysis. Its three basic information types are Task, Concept, and Reference. Tasks are analyzed into steps, with a main goal of identifying steps that are reusable in multiple tasks. Hierarchical task analysis Hierarchical task analysis (HTA) is a task description method and a variant of task analysis. Task description is a necessary precursor for other analysis techniques, including critical path analysis (CPA). HTA is used to produce an exhaustive description of tasks in a hierarchical structure of goals, sub-goals, operations and plans. In HTA, tasks are broken down into progressively smaller units. Operations and plans Operations are the actions performed by people interacting with a system or by the system itself, and plans explain the conditions necessary for these operations. Operations describe the smallest individual task steps in the HTA, i.e. those which cannot be broken down into plans and further operations. They are the individual actions, such as 'visually locate control' or 'move hand to control', which the user must perform in a particular combination to achieve the goal of task completion. Applying The following steps should be followed when conducting a HTA: Define the task under investigation and identify the purpose of the task analysis. The analyst should have some further evaluation methods in mind for which the HTA will be useful and should have reason for needing this type of analysis to be performed. Data collection