If $\text{MASON}$ is coded as $\text{NBTPO}$, then $\text{WORLD}$ is coded as:

Let's analyze the shift pattern between the keyword $\text{MASON}$ and its code $\text{NBTPO}$:
* $\text{M}\stackrel{+1}{\to }\text{N}$
* $\text{A}\stackrel{+1}{\to }\text{B}$
* $\text{S}\stackrel{+1}{\to }\text{T}$
* $\text{O}\stackrel{+1}{\to }\text{P}$
* $\text{N}\stackrel{+1}{\to }\text{O}$

Every letter is shifted forward by exactly $+1$ position in alphabetical order. Applying this identical pattern to $\text{WORLD}$:

* $\text{W}\stackrel{+1}{\to }\text{X}$
* $\text{O}\stackrel{+1}{\to }\text{P}$
* $\text{R}\stackrel{+1}{\to }\text{S}$
* $\text{L}\stackrel{+1}{\to }\text{M}$
* $\text{D}\stackrel{+1}{\to }\text{E}$

Thus, $\text{WORLD}$ is coded as $\text{XPSME}$.