Using FileMaker Pro Advanced > About custom functions (FileMaker Pro Advanced) > Custom Function dependency rules (FileMaker Pro Advanced)
 
Custom Function dependency rules (FileMaker Pro Advanced)
When you copy or import a custom function into a file, FileMaker Pro attempts to resolve any dependencies the function may contain. The following dependency rules apply under different conditions:
If function_a has a dependency on function_b, yet only function_a is copied or imported into a target file that contains a function_b, function_a calls function_b located in the target file, which may cause unexpected results.
If function_a has a dependency on function_b, yet only function_a is copied or imported into a target file, function_a appears enclosed in comment characters (/*<function_definition>*/) in the Manage Custom Functions dialog box, indicating the new function is invalid in the target file.
If function_a has a dependency on function_b, and both function_a and function_b are copied or imported into a target file, function_a will operate as expected.
If function_a has a dependency on function_b, and both functions are copied or imported into a target file that contains an existing function_b, the copied function_b is renamed function_b N. FileMaker Pro updates function_a to call function_b N and function_a operates as expected.
If function_a has a dependency on function_b, and both functions are copied or imported into a target file that contains an existing function_a and function_b, the copied functions are renamed function_a N and function_b M. FileMaker Pro updates function_a N to call function_b M and function_a N operates as function_a in the original file.
If function_a calls itself recursively and it is copied or imported into a target file that contains an existing function_a, FileMaker Pro renames the copied function to maintain the integrity of the dependency.
Related topics 
Using custom functions (FileMaker Pro Advanced)
Importing custom functions (FileMaker Pro Advanced)