On hacklang.org, navigate to the documentation. In the table of contents, find the 'Control Flow' section and then locate the 'Readonly' entry. Based on its brief description provided directly in the table of contents, explain the primary purpose of 'Readonly' in Hack.
Navigate to hacklang.org. Click on the 'Docs' link to go to the documentation page. Scroll down the page to locate the 'Control Flow' section in the table of contents. Identify the 'Readonly' entry under the 'Control Flow' section. Extract the brief description associated with 'Readonly' from the table of contents. State what 'Readonly' is primarily designed for in Hack based on the extracted description.
Successfully navigates to the Hack documentation page. Successfully locates the 'Control Flow' section in the table of contents. Successfully identifies the 'Readonly' entry under 'Control Flow'. States that 'Readonly' is a specialized feature for performantly controlling object mutability.