clarify top bound and how it feeds into rep range check

src/cap-description.adoc

@@ -448,8 +448,8 @@ T[MW - 1:MW - 2] = B[MW - 1:MW - 2] + LCout + LMSB
 Decoding the bounds:
 
 ```
-top:    t = { a[MXLEN - 1:E + MW] + ct, T[MW - 1:0]    , {E{1'b0}} }
-base:   b = { a[MXLEN - 1:E + MW] + cb, B[MW - 1:0]    , {E{1'b0}} }
+top:    t = { 1'b0, a[MXLEN - 1:E + MW] + ct, T[MW - 1:0], {E{1'b0}} }
+base:   b = {       a[MXLEN - 1:E + MW] + cb, B[MW - 1:0], {E{1'b0}} }
 ```
 The corrections c~t~ and c~b~ are calculated as as shown below using the
 definitions in xref:cap_encoding_ct[xrefstyle=short] and
@@ -691,7 +691,7 @@ bounds are formed of two or three sections:
 | EF=1, i.e. E=0 | address[MXLEN:MW] + ct   2+| T[MW - 1:0]
 |==============================================================================
 
-The top described by xref:comp_addr_bounds[xrefstyle=short] is MXLEN+1 bits
+The top bound described by xref:comp_addr_bounds[xrefstyle=short] is MXLEN+1 bits
 wide to allow capabilities to span the whole address space. The address is
 zero-extended by one bit. The malformed check (see
 xref:section_cap_malformed[xrefstyle=short]) ensures that the top never
@@ -717,3 +717,7 @@ xref:section_cap_encoding[xrefstyle=short].
 This gives useful guarantees, such that if an executed instruction is in
 <<pcc>> bounds, then it is also guaranteed that the next linear instruction
 is _representable_.
+
+NOTE: Even though address[MXLEN] in xref:comp_addr_bounds[xrefstyle=short] affects
+ the value of the top bound, it does not have an affect on the _representable range_
+ calculation and so can be excluded from the check.