In C#, you can do:
namespace Blah
{
namespace Foo
{
}
}
Or:
namespace Blah.Foo
{
}
Which should I prefer, if either? The bottom one is somewhat cleaner in terms of braces, but I don't know if it has the same properties.
Both behave equally, and I strongly prefer the second one.
Usually, people prefer having 1 .cs file per class/interface, or at least for groups of similar ones (e.g., all Tuple implementations), which means you usually have 1 namespace in a .cs file anyway.
Nested Namespaces add levels of indentation. Usually, you are already 3 levels deep (namespace, class, method) for each piece of code that you write, so why add even more unnecessary indentations?