Keyword "from" is not a valid keyword in some languages

[mmena1]

Information:

• Prism version: latest from the CDN.
• Plugins: none
• Environment: Browser

Description
Prism incorrectly highlights the "from" word as a keyword in some languages which are not supposed to be highlighted. An example of this is Javascript and C#.

Although in C# is kinda tricky since it is a keyword when using a from-in clause:

func(from: "America", to: "Asia"); // Prism incorrectly highlights "from" as a keyword

from element in list; // no issues here

Example
JSFiddle

[RunDevelopment]

JavaScript:

from is a keyword in JavaScript and Prism highlights it as such.

(source)

We use a little trick to only highlight the from in imports as a keyword: from(?=\s*(?:['"]|$)). The from keyword is guaranteed to be preceded by a string literal, so our regex checks for that.

C#:

As you said, this is tricky. Prism's regex-based highlighting approach is not powerful enough to detect whether from is used as a keyword inside a LINQ query or as a regular identifier elsewhere.

However, I think we could use a similar trick as for JS. The from keyword is guaranteed to be preceded by either a type or an identifier. I'll make a PR for this trick.