# Style Guide > Style guide for writing text. - Filenames should be lowercase. Some top-level files and all `README.md` files are exceptions. - Filenames should be snake_case. - Use American English spelling (e.g., "Capitalize" versus "Capitalise", "color" versus "colour", etc). - Insofar as is possible, spelling and grammar issues should be identified using tools, and, if not caught by a tool, should be identified by human reviewers. - Use the [Oxford comma][oxford-comma] for clarity. - Avoid using personal pronouns in reference documentation (e.g., "I", "you", "we"). - Personal pronouns are acceptable in more colloquial documentation, such as guides. - Prefer using gender-neutral pronouns and mass nouns. For example, - **OK**: "one", "they", "their", "them", "people", "developers" - **NOT OK**: "his", "him", "guys" Exclusive use of female pronoun forms is permitted. - Place end-of-sentence punctuation inside wrapping elements (e.g., periods should be placed inside parentheses and quotes, not after). - Markdown documents must start with a level-one heading, such as in this document. - Use definitions rather than in-lining (e.g., prefer `[link][]` over `[link](http://example.com)`). - References to constructor functions should use PascalCase. - References to constructor instances should use camelCase. - References to functions and methods should use parentheses (e.g., `foo.factory()` versus `foo.factory`).

[oxford-comma]: https://en.wikipedia.org/wiki/Serial_comma