What is the minimum value of "initial-scale" in meta viewport tag?

Question

While experimenting with the meta viewport tag I noticed that any value less than 0.25 for initial-scale is treated as 0.25. E.g. all of the following

<meta name="viewport" content="width=device-width, initial-scale=0.25">  
<meta name="viewport" content="width=device-width, initial-scale=0.1">  
<meta name="viewport" content="width=device-width, initial-scale=0.01">  
<meta name="viewport" content="width=device-width, initial-scale= ">

render the page same. So,

• Is the minimum allowed vale of "initial-scale" in meta viewport tag 0.25?
• What is the default value of initial-scale?
• Why don't initial scale take it's default value, instead of taking 0.25, when blank space is given to initial scale as initial-scale=?

Answer 1

The W3C states

The initial-scale, minimum-scale, and maximum-scale properties

The properties are translated into 'zoom', 'min-zoom', and 'max-zoom' respectively with the following translations of values.

1. Non-negative number values are translated to values, clamped to the range [0.1, 10]
2. Negative number values are dropped
3. yes is translated to 1
4. device-width and device-height are translated to 10
5. no and unknown values are translated to 0.1

Src: https://www.w3.org/TR/css-device-adapt-1/#translate-meta-to-at-viewport

With the above given, the minimum should be 0.1, the default 0.1 and when no value is set, the default is used.

So the browser you tested it on most likely use the default, but since it appears to not go lower than 0.25, as it doesn't in your test cases, one can't say if it does or does not use the default.