Alter column set default doesn't work in T-SQL 2005

Looking to the MSDN help http://msdn2.microsoft.com/en-us/library/ms174123(SQL.100).aspx (Same topic I have in local MSDN Library) I could not understand why following commands did not work:

alter table [Albums] alter column [Comment] set default 'default';
alter table [Albums] alter column [Comment] set not null;

I was getting error message:

Incorrect syntax near the keyword 'set'.

First I found this solution for default:

alter table [Albums] add constraint DF_Albumns_Comment default 'default' for [Comment];

constraint name is optional;

For not null similar solution:

alter table [Albums] add constraint NN_Albumns_Comment check ([Comment] is not null);

produces slightly different result. This new constraint is added over existing table definitions. The definition for column [Comment] is that it still allows nulls.

But then I noticed that online help was in fact for SQL 2008 compact edition, and later I found updated version (February 2008) for SQL 2005
http://msdn2.microsoft.com/en-us/library/ms190273.aspx

Now ther is no option for default here, so solution with new constraint should be used. But for not null constraint I can use this:

alter table [Albums] alter column [Comment] varchar(30) not null;

And no mistery.