Text Concatenation Operator: &
A & B
Evaluates «A» and «B», coerces their element values to text, and concatenates the result.
When concatenating numeric values to text, a number format is required to determine how the numbers should be rendered as text, what precision should be depicted, etc. The number format for the variable or User-Defined Function being evaluated is used. Only the number format for the whole variable is used -- if you have set cell-level formats (such as a different number format for a particular slice), this does not impact the behavior of the number-to-text coercion. If in doubt, you can use the NumberToText function to control the format of converted numbers before applying the & operator.
'Hello' & ' ' & 'world' → 'Hello world'
5 & 2 → '52'
['a', 'b'] & 'c' → ['ac', 'bc']
The need to coerce numbers to text using a particular format often arises. Instead of having to rely on setting the number format for the variable that you are defining for this purpose, you can use the NumberToText function.