AbstractA simple block structure (calledsemiblock) suitable for low‐level languages is presented. This is not a language but a structure, and preserves the high efficiency of the programs written in the ‘host’ languages. The structure offers the localization of label scopes and the capability of constructing control structures such as selection and repetition. The self‐documentability of programs can be increased by the use of Algol‐like formatting of source texts, which the proposed structure allows and encourages the users to use. The relation between the proposed structure and a simple macro facility is