Textual requirements are one of the most common forms of documenting requirements. They are written statements that describe the features and characteristics of a solution, as well as the context and assumptions that affect the requirements. Textual requirements should always address three aspects of the requirements: the capabilities of the solution, the conditions that must exist for the requirements to operate, and any constraints that may hinder the solution. The capabilities of the solution are the functions and behaviors that the solution must perform to meet the stakeholder needs. The conditions are the environmental and organizational factors that affect the requirements, such as regulations, standards, policies, or dependencies. The constraints are the limitations or restrictions that affect the solution, such as budget, schedule, technology, or quality. Reference:
A Guide to the Business Analysis Body of Knowledge (BABOK Guide), Version 3, Chapter 4: Requirements Analysis and Design Definition, Section 4.2: Specify and Model Requirements, p. 119-120.
Business Analysis for Practitioners: A Practice Guide, Chapter 5: Traceability and Monitoring, Section 5.2: Requirements Documentation, p. 111-112.