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diff --git a/design-documents/003-tos-rendering.rst b/design-documents/003-tos-rendering.rst new file mode 100644 index 00000000..5f6d8157 --- /dev/null +++ b/design-documents/003-tos-rendering.rst @@ -0,0 +1,84 @@ +Design Doc 003: ToS rendering +############################# + +Summary +======= + +This document describes how terms of service (ToS) as well as other "legal +agreement documents" are served, represented and rendered. + +Motivation +========== + +Different exchanges and backup/sync providers each have their custom legal +agreement documents. As we don't know all providers and they are not centrally +registered anywhere, these documents can't be hardcoded into wallet +applications. Instead, these service providers expose endpoints that allow +downloading the latest version of these legal agreement documents. + +These documents must be rendered on a variety of platforms in a user-friendly +way. + +Proposed Solution +================= + +The service providers can output legal agreements in various formats, +determined via the ``"Accept: "`` request header. The format provider **must** +support the ``text/plain`` mime type. The format provider **must** support +the ``text/markdown`` mime type. Except for styling and navigation, the +content of each format of the same legal agreement document **should** be the +same. + +Legal documents with mime type ``text/markdown`` **should** confirm to the +`commonmark specification <https://commonmark.org/>`__. + +When wallets render ``text/markdown`` legal documents, they **must** disable +embedded HTML rendering. Wallets **may** style the markdown rendering to improve +usability. For example, they can make sections collabsible or add a nagivation side-bar +on bigger screens. + +It is recommended that the ``text/markdown`` document is used as the "master +document" for generating the corresponding legal agreement document in other +formats. However, service providers can also provide custom versions with more +appropriate styling, like a logo in the header of a printable PDF document. + +Alternatives +============ + +We considered and rejected the following alternatives: + +* Use only plain text. This is not user-friendly, as inline formatting (bold, + italic), styled section headers, paragraphs wrapped to the screen size, + formatted lists and tables are not supported. + +* Use HTML. This has a variety of issues: + + * Service providers might provide HTML that does not render nicely on the + device that our wallet application is running on. + * Rendering HTML inside the application poses security risks. + +* Use a strict subset of HTML. This would mean we would have to define some + standardized subset that all wallet implementations support, which is too + much work. Existing HTML renderers (such as Android's ``Html.fromHTML``) + support undocumented subsets that lack features we want, such as ordered + lists. Defining our own HTML subset would also make authoring harder, as it + forces authors of legal agreement documents to author in our HTML subset, as + conversion tools from other format will not generate output in our HTML + subset. + +* Use reStructuredText (directly or via Sphinx). This at first looks like an + obvious choice for a master format, since Taler is already using reStructuredText + for all its documentation. But it doesn't work out well, since the only maintained + implementation of a parser/renderer is written in Python. Even with the Python implementation + (docutils / Sphinx), we can't convert ``.rst`` to Markdown nicely. + +Drawbacks +========= + +* Markdown parsing / rendering libraries can be relatively large. + +Discussion / Q&A +================ + +* Should the legal agreement endpoints have some mechanism to determine what + content types they support? |