 Specifications can be either "performance-based", whereby the specifier restricts the text to stating the performance that must be achieved by the completed work, "prescriptive" where the specifier states the specific criteria such as fabrication standards applicable to the item, or "proprietary", whereby the specifier indicates specific products, vendors and even contractors that are acceptable for each workscope.In addition, specifications can be "closed" with a specific list of products, or "open" allowing for substitutions made by the Contractor.Most construction specifications are a combination of performance-based and proprietrary types, naming acceptable manufacturers and products while also specifying certain standards and design criteria that must be met.