CDS to DDL: clarify treatment of expressions

[stewsk]

No description provided.

[renejeglinsky]

Suggested change

	Note that expressions in CDS models are _not_ treated in a database-agnostic way. In other words, they are not rewritten
	into database-specific equivalents; instead, they are carried over one-to-one into the DDL.
	You therefore need to ensure that any expression you write in your CDS model works across all databases you use.
	See also [Database-Specific Models](#database-specific-models).
	Expressions in CDS models are _not_ treated in a database-agnostic way. The compiler does not rewrite them into database-specific equivalents. Instead, it carries them over directly into the DDL. Ensure that any expression you write in your CDS model works across all databases you use. For more information, see [Database-Specific Models](#database-specific-models).