Syntax highlighting works fine (on Github):
```html
<script scr='/foo.js'>
```
Is it possible to use syntax highlighting without fencing?
For example, `<script scr='/foo.js'>`
It's unclear from your question whether you want inline syntax highlighting on the github.com site itself, or whether you want inline syntax highlighting on an arbitrary site that happens to support the github variant of markdown.
If it's the former, then, no, github.com won't currently add syntax highlighting to inline code.
If it's the latter, then it depends on the particular tool that you're using to convert markdown to HTML. Pandoc, for example does support syntax highlighting for inline code.
You can't have syntax highlighting on github with inline code blocks or space-indenting, only with fencing.
ruby`puts :OK`