[Tutor] Can re do this?

[R. Alan Monroe]

Given a test file like:
The quick brown fox jumps over the lazy log
Another test line lazy dog

I want to match lines containing "the lazy dog" (line 2 would not
match). This I can do. I then want to change "lazy" to "xxx" (in line
1 but not line 2). This is where I'm getting stuck. I can't figure out
how to replace just a subset of "the lazy dog", which is itself, a
subset of the entire line.

Alan