Even the simplest possible webkit browser I know,
Code:
#!/usr/bin/env python
if __name__ == "__main__":
import sys
import gtk
import webkit
window = gtk.Window(gtk.WINDOW_TOPLEVEL)
webview = webkit.WebView()
window.add(webview)
if (len(sys.argv) > 1):
webview.open(sys.argv[1])
else:
webview.open("http://www.google.com/")
window.show_all()
gtk.main()
which requires only python and pywebkitgtk, allows selecting text on a webpage. The selection is automatically put onto the PRIMARY clipboard, too.
Edit: This is to say that this is all built-in to webkit. If a webkit browser does not allow this, it must have gone to pretty extraordinary lengths to specifically disallow it. I'd say it is safe to assume all webkit browsers allow it.