Nowadays, browsers on mobile devices such as mobile phones or tablets have a double-click to enlarge setting by default. How can I prevent double-clicking to zoom in?
The viewport meta is provided on the Mobile page, which can be used to set zoom. But before using viewport, you need to change the document type of the page to Mobile type. The usual page DTD is XHTML or simple HTML5 declaration. Mobile devices should use the following declaration.
If you need more detailed information about viewport, please refer to MDN
https://developer.mozilla.org/en-US/docs/Mobile/Viewport_meta_tag
It seems that the DTD can only be declared as HTML5, and the viewport tag is added below