I added this because the main suggestion in this section is to ignore the lack of mq support in oldIE. This would cause problems if the default styles were for mobile.
Added warning about mobile first
I don't think we should advise serving a mobile/narrow layout to a desktop browser just because it's an older Internet Explorer release. This is completely dependent on the circumstances: what percentage of visitors uses these versions, are there any requirements/limitations in functionality (i.e. mobile-targeted layouts tend to prefer touch input over mouse input), and concessions done in terms of accessibility and readability.
Oh, maybe you misunderstood what I added here. Let me explain:
In the original text, it explains that MQs don't work in oldIE, so devs are advised to 'make their peace with that'. But, this is problematic if they are using a mobile-first approach where the default styles are for a narrow screen. So I added a reminder to make sure that a separate stylesheet is served for oldIE that gives a regular layout (non-mobile). So I was not encouraging serving a mobile/narrow layout to a desktop browser; I was encouraging some caution on taking the 'make your peace with it' advice while using a mobile-first approach, because this would end up serving a narrow layout to oldIE.
Does that make it more clear what I'm trying to say?
@impressivewebs I get what you are trying to say, but I feel it is too little to state it so simply. Perhaps a rewrite would be in order?
Well, currenty it says:
"If you choose a mobile first 'bottom-up' approach where your default styles target the smallest screens first, then be sure to give oldIE separate styles."
How about instead:
"A caution is in order: If you choose a mobile first approach, you'll be targeting smallest screens first, then the different media queries will take effect as the window/device size increases. But if the browser doesn't support media queries and you don't use a polyfill, then the 'mobile first' styles will be applied to certain desktop browsers."
Feel free to add that in or make any changes to make it sound more clear.
Thanks! I have updated it 73ac561