Another form of concatenation is the replication operation. The first
expression shall be a non-zero, non-X and non-Z constant expression, the
second expression follows the rules for concatenations. This example replicates
"w" 4 times.

{4{w}} // This is equivalent to {w, w, w, w}

a[31:0] = {1`b1, {0{1`b0}} };    //illegal. RHS
becomes {1`b1,;

a[31:0] = {1`b1, {1`bz{1`b0}} }; //illegal. RHS becomes {1`b1,;

a[31:0] = {1`b1, {1`bx{1`b0}} }; //illegal. RHS becomes {1`b1,;

The comments on the three examples of illegal concatenations look strange.

"RHS becomes {1 b1,;" looks cut off.

I propose to just leave them as "illegal". Anyone who reads the
preceding paragraph will immediately understand the reason. The existing
comments is just confusing.

-- 
Shalom Bresticker                           Shalom.Bresticker@motorola.com
Design & Reuse Methodology                             Tel: +972 9 9522268
Motorola Semiconductor Israel, Ltd.                    Fax: +972 9 9522890
POB 2208, Herzlia 46120, ISRAEL                       Cell: +972 50 441478

"The devil is in the details."