Supported browser rendering

The HTML renderer supports a document-oriented subset of browser rendering for reports, invoices, statements, forms, and labels. Use the overview below to choose a layout, then follow the linked reference for supported values and restrictions.

Supported behavior

Area	What you can use
HTML and text	Headings, paragraphs, inline emphasis, lists, links, character references, and static form controls
CSS	Supported selectors, the cascade, custom properties, generated content, colors, borders, and spacing
Sizing and layout	Block and inline layout, flexbox, grid, size constraints, text wrapping, and relative or absolute positioning
Tables	Column sizing, spanning cells, nested tables, repeated headers, and separate or collapsed borders
Images and backgrounds	JPEG, supported PNG formats, self-contained SVG, image fitting, and background sizing and repetition
Pages	Page sizes and margins, automatic and explicit breaks, running headers and footers, and page numbers
Fonts	Bundled DejaVu Sans, registered TrueType fonts, optional system-font discovery, and glyph fallback

This subset does not include JavaScript, interactive PDF form fields, or full browser layout and typography. See Known limits before adapting a browser template. The renderer reports unsupported HTML and CSS through the diagnostic contract.

Visual parity

We compare rendered documents with Chromium at 72 DPI. Every fixture enforces a ceiling of 3% differing pixels or less. A pixel differs when at least one RGB channel differs by more than 12 out of 255. Each fixture also checks the page count and its existing average channel-delta limit.

The comparison uses the installed fonts without forced font aliases. Results vary with the operating system, installed fonts, and browser version; the threshold applies to the tested fixtures, not every document or environment.

These percentages describe visual comparisons, not a percentage of browser features supported. Start with the rendering examples for working templates.

Measured comparisons

These historical measurements used forced font aliases to align native and Chromium font selection. They do not represent the current default-font setup.

The table records the maximum changed-pixel ratio and maximum average channel delta across each fixture's pages, before and after the rendering corrections. Measurements used Chromium 152.0.7977.82 and Poppler 26.08.0. Values are fractions, rounded to six decimal places. Average deltas use channel differences divided by 255. Page counts match Chromium in both runs. Chromium and Poppler versions can change rasterization, so the tests remain the source of truth for a local build. Each comparison writes its measurements to tmp/browser_parity/<fixture>/stats.exs.

Fixture	Before changed	After changed	Before average	After average	Pages
`absolute_positioning`	0.000000	0.000000	0.000000	0.000000	1
`background_images`	0.005026	0.005026	0.000924	0.000923	1
`block_box_model`	0.013326	0.003759	0.006966	0.001071	1
`border_style_variants`	0.040866	0.013835	0.015812	0.005687	1
`box_sizing_and_margins`	0.048978	0.004186	0.014912	0.002189	1
`break_variants`	0.014273	0.005261	0.008917	0.003360	4
`cmyk_jpeg_colors`	0.225000	0.000000	0.024118	0.000000	1
`computed_custom_properties`	0.000000	0.000000	0.000000	0.000000	1
`css_cascade_selectors`	0.025316	0.009598	0.006620	0.002997	1
`css_remaining_supported_values`	0.047344	0.004182	0.013802	0.001858	1
`display_lists_and_inline_block`	0.020615	0.008614	0.009093	0.003884	1
`distributed_gaps`	0.008247	0.008247	0.005498	0.005498	1
`empty_flex_height`	0.000000	0.000000	0.000000	0.000000	1
`flex_direction_and_justification`	0.039538	0.013691	0.017569	0.007099	1
`flex_grid_alignment`	0.022682	0.004863	0.009078	0.002474	1
`fonts_and_print_media`	0.010392	0.004778	0.003419	0.001776	1
`generated_content_counters`	0.021549	0.006030	0.007696	0.001746	1
`government_application_form`	0.033214	0.019625	0.011544	0.006463	1
`grid_explicit_sizes`	0.000000	0.000000	0.000000	0.000000	1
`grid_span_end`	0.000000	0.000000	0.000000	0.000000	1
`grid_sparse_placement`	0.000000	0.000000	0.000000	0.000000	1
`grid_tracks_and_placement`	0.019325	0.004126	0.009635	0.002252	1
`hidden_tables`	0.000000	0.000000	0.000000	0.000000	1
`html_semantics_typography`	0.047726	0.009228	0.023937	0.005865	1
`image_object_fitting`	0.005234	0.002049	0.002474	0.000532	1
`images_data_uris`	0.026862	0.006088	0.013614	0.003376	1
`inline_positioning`	0.000699	0.000157	0.000139	0.000036	1
`inline_text_flow`	0.010324	0.007043	0.003267	0.002320	1
`invoice_012`	0.044961	0.003449	0.012295	0.001212	1
`layout_compositions_remaining`	0.045748	0.018748	0.024946	0.009580	1
`links_entities_and_protocols`	0.018426	0.005234	0.010822	0.003469	1
`material_requisition`	0.039841	0.012483	0.010872	0.002522	2
`multi_page_report_012`	0.027334	0.007759	0.007918	0.002245	2
`nested_table_collapsed_borders`	0.025919	0.010732	0.014692	0.005843	1
`nested_table_grid_flex`	0.023053	0.011168	0.011224	0.005438	1
`page_furniture`	0.006598	0.005560	0.002504	0.002144	2
`page_geometry_asymmetric`	0.002973	0.000680	0.001405	0.000343	1
`page_rules_landscape`	0.000928	0.000928	0.000536	0.000536	1
`pagination_breaks`	0.004403	0.000126	0.002268	0.000020	2
`paragraph_pagination`	0.014722	0.000000	0.002449	0.000000	2
`png_transparent_color`	0.000000	0.000000	0.000000	0.000000	1
`purchase_order`	0.044869	0.014795	0.013453	0.003071	1
`quoted_at_rules`	0.003071	0.000710	0.000562	0.000135	1
`quoted_variables`	0.000000	0.000000	0.000000	0.000000	1
`root_absolute_pagination`	0.000000	0.000000	0.000000	0.000000	2
`statement_012`	0.033536	0.012086	0.011265	0.002704	1
`static_form_controls`	0.009466	0.008300	0.003197	0.003086	1
`stock_sticker`	0.044596	0.002616	0.007420	0.000380	1
`system_font_inheritance`	0.013080	0.010256	0.003986	0.003182	1
`table_collapsed_borders`	0.032956	0.010788	0.016993	0.004559	1
`table_column_layout`	0.042236	0.003707	0.024260	0.001972	1
`table_header_near_page_row`	0.035185	0.006620	0.015151	0.004810	2
`table_pagination_headers`	0.015746	0.001754	0.008630	0.001063	2
`table_rowspan_tfoot`	0.022139	0.006373	0.010748	0.002237	1
`table_separate_borders`	0.024107	0.005216	0.014058	0.002555	1
`text_style_variants`	0.041601	0.010272	0.018766	0.004529	1
`trim_card`	0.052570	0.015661	0.018627	0.003926	1
`units_and_sizing`	0.032484	0.015789	0.009215	0.003437	1
`unsupported_glyph_replacement`	0.012193	0.012026	0.006146	0.006101	1
`weight_inheritance`	0.045833	0.000000	0.018333	0.000000	1
`whitespace_pre_line`	0.024448	0.005610	0.008130	0.001844	1
`zero_font_size`	0.014896	0.000000	0.003094	0.000000	1

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