A query can be broken over multiple lines to make it more readable. For example:
{
FILTER(
     {TM1FILTERBYLEVEL( {TM1SUBSETALL( [Product] )}, 0)},
       Test2.([Rate Measures].[Rate]) = 19
      )
}
is more readable than having the whole query in one line. The actual filter section is more easily read and modified now by having it on a line by itself.

Note that references to members usually have the dimension name as a prefix. For example,
{ {[Product].[Retail].Children} }
In fact the dimension name is optional – but only if the member name (Retail in this case) is completely unique within the entire server - i.e. there are no cubes, dimensions or members with that exact name. For example this is the same query with the dimension name omitted:
{ {[Retail].Children} }
Which would work in the context of the sample application used by this document but would be risky in a real-world application. The error message received when forgetting to specify the prefix would be something like, “Level or member name “[Retail]” ambiguous: found in dimensions…” and then it goes on to list the various dimensions in which the non-unique member name can be found, which is very helpful. It is therefore certainly safest and most performant to always use the dimension prefix.

The use of square brackets can sometimes seem a bit arbitrary when reading examples of MDX queries. The fact is that an OLAP object name (e.g. cube name, dimension name, member name) must be enclosed in square brackets only if it contains a space, starts with a number or is an MDX reserved word (e.g. Select). However, sometimes it can be simpler to decide to always use brackets so similar queries can be compared side by side more easily.

The exact definition of a member in TM1 is almost always expressed as [Dimension Name].[Member Name] and no more. In other products that also use MDX as a query language (such as Microsoft Analysis Services) you may notice that queries specific the full ‘path’ from the dimension name through the hierarchy down to the member name, for example:
[Date].[2009].[Q1].[Feb].[Week 06]
This can also be written as [Date].[2009^Q1^Feb^Week 06]
The reason for this is that other products may not require every member name to be unique since each member has a context (it’s family) to enable it be uniquely identified, which is why they need to know exactly which Week 06 is required since there may be others (in 2008 for instance in the above example). TM1 requires all member names, at any level (and within Aliases) to be completely unique within that dimension. TM1 would need you to make Q1, Feb and Week 06 more explicit in the first place (i.e. Q1 2009, Feb 2009, Week 06 2009) but you can then just refer to [Date].[Week 06 2009].

Finally, case (i.e. capital letters versus lower case) is not important with MDX commands (e.g. Filter or FILTER, TOPCOUNT or TopCount are all fine) but again you may prefer to adopt just one style as standard to make it easier to read.