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The lead section (also known as the lead, introduction, or intro) of a PetroWiki topic page is the section before the table of contents and the first heading. The lead serves as an introduction to the topic page and a summary of its most important aspects. The lead should be able to stand alone as a concise overview. It should define the topic, establish context, explain why the topic is notable, and summarize the most important points.
It is the first part of the topic page most people read, and many only read the lead. Consideration should be given to creating interest in reading more of the topic page, but the lead should not "tease" the reader by hinting at content that follows. Instead, the lead should be written in a clear, accessible style with a neutral point of view; it should ideally contain no more than four well-composed paragraphs and be carefully sourced as appropriate.
Introductory text: As explained in more detail below, all but the shortest topic pages should start with introductory text (the "lead"). The lead should establish significance, include mention of consequential or significant criticism or controversies, and be written in a way that makes readers want to know more. The appropriate length of the lead depends on that of the topic page, but should normally be no more than four paragraphs. The lead itself has no heading and, on pages with more than three headings, automatically appears above the table of contents, if present.
Provide an accessible overview. The lead section should briefly summarize the most important points covered in a topic page in such a way that it can stand on its own as a concise version of the topic page. It is even more important here than in the rest of the topic page that the text be accessible. Consideration should be given to creating interest in the topic page. Avoid lengthy paragraphs and over-specific descriptions, since greater detail is saved for the body of the topic page. In general, introduce useful abbreviations, but avoid difficult to understand terminology and symbols. Mathematical equations and formulas should be avoided when they conflict with the goal of making the lead section accessible to as broad an audience as possible. Where uncommon terms are essential, they should be placed in context, linked and briefly defined. The subject should be placed in a context familiar to a normal reader. Readers should not be dropped into the middle of the subject from the first word; they should be eased into it.
According to the policy on due weight, emphasis given to material should reflect its relative importance to the subject, according to published reliable sources. This is true for both the lead and the body of the topic page. If there is a difference in emphasis between the two, editors should seek to resolve the discrepancy. Significant information should not appear in the lead if it is not covered in the remainder of the topic page, although not everything in the lead must be repeated in the body of the text. This admonition should not be taken as a reason to exclude information from the lead, but rather to harmonize coverage in the lead with material in the body of the topic page.
The first paragraph should define the topic with a neutral point of view, but without being overly specific. It should establish the context in which the topic is being considered by supplying the set of circumstances or facts that surround it.
The first sentence should tell the nonspecialist reader what the subject is. If possible, the page title should be the subject of the first sentence. However, if the topic page title is merely descriptive, the title does not need to appear verbatim in the main text. When the page title is used as the subject of the first sentence, it may appear in a slightly different form, and it may include variations, including synonyms. Similarly, if the title has a parenthetical disambiguator, the disambiguator should be omitted in the text. If its subject is definable, then the first sentence should give a concise definition: where possible, one that puts the topic page in context for the nonspecialist. Similarly, if the title is a specialised term, provide the context as early as possible. Redundancy must be kept to a minimum in the first sentence. Use the first sentence of the topic page to provide relevant information which is not already given by the title of the topic page. Remember that the title of the topic page need not appear verbatim in the lead.
Abbreviations and synonyms
If the subject of the page has a common abbreviation or more than one name, the abbreviation (in parentheses) and each additional name should be in boldface on its first appearance.
The opening sentence should provide links to the broader or more elementary topics that define the page's topic or place it into the context where it is notable. In a topic page about a technical or jargon term, the opening sentence or paragraph should normally contain a link to the field of study that the term comes from. Exactly what provides the context needed to understand a given topic varies greatly from topic to topic.
Scope of topic page
In some cases the definition of the topic in the opening paragraph may be insufficient to fully constrain the scope of the topic page. In particular, it may be necessary to identify material that is not within scope. These explanations may best be done at the end of the lead to avoid cluttering and confusing the first paragraph. This and other similar information in the lead is not expected to appear in the body of the topic page.
The appropriate length of the lead section depends on the total length of the topic page. As a general guideline—but not absolute rule—the lead should usually be no longer than four paragraphs. The length of the lead should conform to readers' expectations of a short, but useful and complete, summary of the topic. A lead that is too short leaves the reader unsatisfied; a lead that is too long is difficult to read and may cause the reader to lose interest halfway. The following suggestions about lead length may be useful:
|Topic page length||Lead length|
|Fewer than 15,000 characters||One or two paragraphs|
|15,000–30,000 characters||Two or three paragraphs|
|More than 30,000 characters||Three or four paragraphs|