PHP Manual: variant

Description

mixed variant_add ( mixed left, mixed right )

Adds left to right using the following rules (taken from the MSDN library), which correspond to those of Visual Basic:

Table 1. Variant Addition Rules

If	Then
Both expressions are of the string type	Concatenation
One expression is a string type and the other a character	Addition
One expression is numeric and the other is a string	Addition
Both expressions are numeric	Addition
Either expression is NULL	NULL is returned
Both expressions are empty	Integer subtype is returned

See also variant_sub().

Note: As with all the variant arithmetic functions, the parameters for this function can be either a PHP native type (integer, string, floating point, boolean or NULL), or an instance of a COM, VARIANT or DOTNET class. PHP native types will be converted to variants using the same rules as found in the constructor for the VARIANT class. COM and DOTNET objects will have the value of their default property taken and used as the variant value.
The variant arithmetic functions are wrappers around the similarly named functions in the COM library; for more information on these functions, consult the MSDN library. The PHP functions are named slightly differently; for example variant_add() in PHP corresponds to VarAdd() in the MSDN documentation.