sentences:  Early syntax-directed source code editors included Interlisp-D (for Lisp’s limited syntax) and Emily (for PL/I’s rich syntax).A syntax-directed editor may treat grammar rules as generative (e.g., offering the user templates that correspond to one or more steps in a formal derivation of program text) or proscriptive (e.g., preventing a phrase of a given part of speech from being moved to a context where another part of speech is required) or analytic (e.g., parsing textual edits to create a structured representation).Structure editing features in source code editors make it harder to write programs with invalid syntax.