2.1.588 Part 4 Section 2.18.91, ST_TabJc (Custom Tab Stop Type)
a. The standard states that the decimal value specifies that the current tab stop shall result in a location in the document where all following text is aligned around the first decimal character in the following text runs.
In Word, if the value is decimal, the tab stop results in a location in the document where all following text is aligned around the first decimal separator in the following text runs.
b. The standard does not state how to interpret the decimal attribute if there is no decimal separator.
Word aligns text around the implicit decimal separator after the last digit of the first numerical value appearing in the following text if there is no decimal separator.