docs: Add loose mode to README

README.md

@@ -6,6 +6,10 @@ pip-requirements-js strictly adheres to [pip's documentation of the requirements
 
 ## API
 
+### Full extraction 
+
+Full extractions means complete requirement info, such as spec-conforming version constraints and complete validation of the environment marker tree.
+
 To extract all the requirements from a given file, use
 ```typescript
 parsePipRequirementsFile(fileContent: string): Requirement[]
@@ -15,12 +19,20 @@ To extract a requirement from a given line, use
 ```typescript
 parsePipRequirementsLine(lineContent: string): Requirement | null
 ```
-(note that `null` will be returned if the line is empty)
+(null is returned for lines validly lacking a requirement, e.g. empty or comment-only)
 
 In both cases a `RequirementsSyntaxError` will be thrown if the provided content contains invalid syntax.
 
 To make use of the resulting data, look up what `Requirement` is made up of in [`types.ts`](https://github.com/Twixes/pip-requirements-js/blob/main/src/).
 
+### Loose extraction
+
+There is also a loose mode, which is oriented for processing partially-written requirements. This is useful when handling live code editor input.
+
+`parsePipRequirementsFileLoosely` and `parsePipRequirementsLineLoosely` work the same as their full versions, except they return `LooseProjectNameRequirement` in place of `Requirement`. This means that URL-based requirements are skipped, as are requirements/constraints files.
+
 ## Internals
 
 pip-requirements-js is built with the robust parser generator [Ohm.js](https://github.com/ohmjs/ohm) – the core of this library is the [pep-508.ohm](https://github.com/Twixes/pip-requirements-js/blob/main/src/pep-508.ohm) grammar, which is an Ohm port of [PEP 508's complete dependency specification grammar](https://peps.python.org/pep-0508/#complete-grammar) (originally defined for Parsley), with some pip-specific additions (such as the `-r extra-requirements.txt` syntax). This ensures the greatest possible compatibility with what pip itself does.
+
+This library was built as a backend for the [PyPI Assistant](https://marketplace.visualstudio.com/items?itemName=twixes.pypi-assistant) VS Code extension.