Authoring expressions directly using the compositional grammar, even by hand in a text editor, is useful for situations in which expressions must be defined which don't necessarily conform to a consistent structure. To use this technique, the user must be familiar with the basic features of the Compositional Grammar syntax, please see Compositional Grammar - Specification and Guide. 

There are, however, a number of ways in which a dedicated Compositional Grammar editing tool rather than a generic text editor can better support the user while creating expressions, including:

• Validate the syntactical correctness of the expression as it is authored
• Check the expression for conformance against the concept model
• Automatically populate or correcting the terms used for each part of the expression
• Provide integrated tools to search the SNOMED CT hierarchy for concepts to include in the expression
• Suggest the set of valid operators or characters that may be used at a given point in the expression
• Show any inferable relationships, parents, and/or child concepts
• Indicate if there is an equivalent pre-coordinated concept

When creating expressions using the compositional grammar, it is the responsibility of the author of the expression to ensure the clinical validity of the expression, and ensure that the expression syntax, the concept model and the editorial rules are followed.