EinFormatUS

The two ways a US Employer Identification Number is written: bare digits or dashed.

An EIN (Employer Identification Number) is the nine-digit tax id the IRS gives US businesses. People write it two ways: nine bare digits, "123456789", or the usual dashed form, "12-3456789". EinFormatUS names those layouts, and it answers two separate questions on the EIN methods: which layout the input must arrive in, and which shape the result comes back in.

Members

Member	Meaning
Any	No constraint. As an input rule it accepts both layouts; as an output shape it returns the number in whichever layout it arrived in. The default input rule.
Digits	Nine bare digits: "123456789".
Dashed	The usual written form — a two-digit prefix, a hyphen, seven digits: "12-3456789". The default output shape.

Where it is used

Only CkUS takes it. Ein takes the enum twice: format says which layout the input must match (defaults to Any), and output says which shape comes back (defaults to Dashed; pass Digits for storage). EinMask takes an output parameter too — the shape it masks in; there Any keeps a valid value's own layout and falls back to the dashed shape for the fully masked placeholder.

Quick look

using SafeCoder.CommonKit;
using SafeCoder.CommonKit.Enums;

CkUS.Ein("123456789");            // -> "12-3456789"  (any layout in, dashed out — the defaults)

CkUS.Ein(
    input: "12-3456789",
    output: EinFormatUS.Digits
);                                // -> "123456789"  (bare digits, ready for storage)

CkUS.Ein(
    input: "12-3456789",
    format: EinFormatUS.Digits
);                                // -> ""  (the input had to be bare digits, so the dashes reject it)