You would write "1 million" or "1M". When abbreviated, capitalization is necessary, but by itself, "million" is lowercase.
capitalizemytitle.com explains this:
...million, billion, hundred, thousand are NOT capitalized, and neither are the words “billionaire” or “millionaire” as they are considered to be professions, and they ...
This is likely answered by your style guide. For example, in Chicago Style, there is no space (“usually”). In AP, this type of abbreviation is only allowed in headlines for M and B and doesn’t have a space either.
I would argue against the use of "is" to describe the relationship. There are too many usages of "is" to allow it to be interpreted with the precision that technical writing must have.
This is overly fussy, but after decades of trying to communicate technical details to non-technical audiences, I feel totally justified.
For an exact match,...
Your first suggestion looks fine. It doesn't seem likely to be misconstrued. There are other similar sentences that would convey the same information in slightly different words, such as:
This tag is assigned if FieldName is Value
This tag is assigned when field FieldName is Value
This tag is assigned if field: FieldName is Value
This tag is assigned if ...
I don't know of a specific way to diagram your structure, but I have a few ideas. My ideas aren't perfect, and most of it requires you brainstorming stuff, but I hope it helps nonetheless (or at least gives you a start).
The best option would be to download a complex software to help you with this (I won't point you to any, but there are lots out there).
The filename is irrelevant. If I have my resume as a Word document, and I rename it to bohemian-rhapsody.jpg, then it is still my resume and not a recording of Bohemian Rhapsody, and it is still a Word document, not a "JPEG" file.
For example, "The platform will be able to process multiple image formats such as..."
If you want to talk ...