Support custom HTML element tags in template syntax

[ankhers]

Describe the bug
I am attempting to include the @tailwindplus/elements package. This will give me a handful of custom HTML elements that I can use to build my application. At least some of the custom elements have the - character in the name. e.g., <el-dialog>. Full error below

== Compilation error in file lib/my_app_web/main_layout.ex ==
** (Hologram.TemplateSyntaxError)

Reason:
Unknown reason.

Hint:
Please report that you received this message here: https://github.com/bartblast/hologram/issues
and include a markup snippet that will allow us to reproduce the issue.

ss="h-full">\n    <el-dialog></el-dialog>\n
                     ^

status = :start_tag

token = {:symbol, "-"}

context = %Hologram.Template.Parser.Context{attribute_name: nil, attribute_value: [], attributes: [], block_name: nil, delimiter_stack: [], node_type: :tag, prev_status: :start_tag_name, processed_tags: [{:text, "\n    "}, {:start_tag, {"body", [{"class", [text: "h-full"]}]}}, {:text, "\n  "}, {:end_tag, "head"}, {:text, "\n  "}, {:self_closing_tag, {"Runtime", []}}, {:text, "\n    "}, {:end_tag, "title"}, {:text, "My App"}, {:start_tag, {"title", []}}, {:text, "\n    "}, {:self_closing_tag, {"meta", [{"name", [text: "csrf-token"]}, {"content", [expression: "{Phoenix.Controller.get_csrf_token()}"]}]}}, {:text, "\n    "}, {:self_closing_tag, {"meta", [{"name", [text: "viewport"]}, {"content", [text: "width=device-width, initial-scale=1"]}]}}, {:text, "\n    "}, {:self_closing_tag, {"meta", [{"charset", [text: "utf-8"]}]}}, {:text, "\n    "}, {:start_tag, {"head", []}}, ...], ...}

    (hologram 0.6.6) lib/hologram/template/parser.ex:1064: Hologram.Template.Parser.raise_error/5
    (hologram 0.6.6) lib/hologram/template.ex:22: Hologram.Template.dom_ast/1
    (hologram 0.6.6) lib/hologram/template.ex:40: Hologram.Template.build_holo_sigil_ast/1
    (hologram 0.6.6) expanding macro: Hologram.Template.sigil_HOLO/2
    (my_app 0.1.0) lib/my_app_web/main_layout.ex:7: MyAppWeb.MainLayout.template/0

Reproduction Repository
Please provide a link to a minimal reproduction repository forked from Hologram Skeleton: https://github.com/bartblast/hologram_skeleton
Repository URL:
Not including a repo as this is not specific to my setup. I can create one if need be.

To Reproduce
Steps to reproduce the behavior:

1. Include a - character in any HTML element

Expected behavior
https://developer.mozilla.org/en-US/docs/Web/API/Web_components/Using_custom_elements#using_a_custom_element -- This should be valid.

Screenshots
N/A

Environment information

• Hologram version: 0.6.6
• Elixir version: 1.19.5
• Erlang/OTP version: 28
• Node.js version: 24.13.0
• Operating System: NixOS 25.11
• Browser (if applicable):

Additional context
N/A

[bartblast]

Since the HOLO template syntax is not strictly HTML, I'm categorizing this as an enhancement to support custom HTML element tags.

Supporting custom elements will likely also require some form of JS interop (though I'm not 100% sure yet), but coincidentally JS interop is the focus of this minor release (#702).