lexical - Context free grammar syntax -

i'm trying clarify following context-free grammar:

if i've got following,

s->t0t 

if there 2 possible values t ie.

t-> 1t | 1 

do have use same value when substituting both ts, so:

t0t becomes (1t)0(1t) => 1t01t 

or can use different values each t, so:

tot becomes (1t)0(1) => 1t01 

there no relationship between 2 ts. restriction had same make grammar not context-free, since replacement of t in context-free grammar independent of context. hence "context-free".