Did spell checking on level-ext chapter

src/level-ext.adoc

@@ -137,7 +137,7 @@ NOTE: if W=0 or C=0 then SL is irrelevant
 
 [#section_ext_cheri_multiple_levels]
 === Extending {cheri_levels_ext_name} to more than two levels
-When `LVLBITS>1`, the behaviour of <<ACPERM>> can no longer use masking to adjust the <<section_cap_level>> or <<sl_perm>>, but instead must perform an integer minimum operation on those `LVLBITS`-wide fields.
+When `LVLBITS>1`, the behavior of <<ACPERM>> can no longer use masking to adjust the <<section_cap_level>> or <<sl_perm>>, but instead must perform an integer minimum operation on those `LVLBITS`-wide fields.
 The <<section_cap_level,CL>> field of the resulting capability is set to `min(rs2[CL], cs1[CL])`  (equivalent to `rs2[CL] & cs1[CL]` for `LVLBITS=1`).
 Similarly, <<sl_perm>> is set to `min(rs2[SL], cs1[SL])` (equivalent to `rs2[SL] & cs1[SL]` for `LVLBITS=1`).