One of the harder things to do in Adobe InDesign, surprisingly for a page layout tool, is to create multilevel or outline format numbered lists. The right way to accomplish this, according to the folks at Adobe, is to create a Style for every level of the list you’d like to have! Here are Adobe’s instructions on how to do so (This content is taken directly from https://helpx.adobe.com/indesign/using/bullets-numbering.html#create_multi_level_lists):
To create a running list—a list that is interrupted by other paragraphs or that spans multiple stories or documents—create a paragraph style and apply the style to paragraphs that you want to be part of the list. For example, to create a running list of the tables in your document, create a paragraph style called Tables, make a defined list part of the style, and then apply the Tables paragraph style to all paragraphs you want in your Table list.
I want to point out that if this document is a fixed set of standards but will be amended in later editions, then autonumbers will increment, which is a bad idea. In legal documents, numbers are usually static, and deletions are struck-through, not deleted, to preserve the original numbering, so that older and newer editions can be compared number-by-number. Inserted and appended content would need to be manually numbered. You may want to create the first edition with autonumbering, then convert the numbered list numbers to text, to avoid unwanted renumbering in future editions.
And what all did I forget to do? I forgot to go to 'Styles', 'Paragraph Styles', and I went, right click 'Redefine' because I've reverted to what it was before. So that's page numbering, we used A, B, C, D at the beginning. And we're going to use 1, 2, 3, 4, 5 for the rest of it. The only trouble happens, is when you go 'File', 'Print' now, and you're like, "Hmm." "I want to print pages." and you're not too sure. So what I have to do is go to A, through to 30. So it will include A, B, C, D, E, and all the way through the numbers. What if I just need A, B, or if I just print 1-30? It's going to skip out these first pages. That's just something to be aware of when you're printing, or making PDFs, that the page numbering is a little bit stranger now that we've gone and messed around with the page numbering.
Select the text frame with the Selection Tool (V, Escape) and go to Edit > Copy and Edit > Paste. Manoeuvre this second text frame onto the left-hand page in a mirrored position. InDesign will provide pop-up guidelines once the text frame lines up exactly with the frame on the right-hand page. Once your happy with the positioning, select the Type Tool (T) and adjust the orientation of the text to Align Left from the Character Formatting Controls panel, as before.
A multi-level list is a list that describes hierarchical relationships between the list paragraphs. These lists are also called outline lists because they resemble outlines. The list’s numbering scheme (as well as indentations) show rank as well as how items are subordinate to one another. You can tell where each paragraph fits in the list with respect to the paragraphs before and after it. You can include up to nine levels in a multi-level list.