You need to read the actual license "legalese", not the "human-readable" summary. <a href="http://creativecommons.org/licenses/by/3.0/legalcode">Here is the relevant section</a>:<div><br></div><blockquote class="webkit-indent-blockquote" style="margin: 0 0 0 40px; border: none; padding: 0px;">
<div><meta http-equiv="content-type" content="text/html; charset=utf-8"><span class="Apple-style-span" style="color: rgb(85, 85, 85); font-family: TeXGyreAdventorRegular, 'Century Gothic', 'URW Gothic L', sans-serif; font-size: 13px; line-height: 18px; ">If You Distribute, or Publicly Perform the Work or any Adaptations or Collections, You must, unless a request has been made pursuant to Section 4(a), <strong style="padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">keep intact all copyright notices for the Work and provide, reasonable to the medium or means You are utilizing: (i) the name of the Original Author (or pseudonym, if applicable) if supplied, and/or if the Original Author and/or Licensor designate another party or parties (e.g., a sponsor institute, publishing entity, journal) for attribution ("Attribution Parties") in Licensor's copyright notice, terms of service or by other reasonable means, the name of such party or parties; (ii) the title of the Work if supplied; (iii) to the extent reasonably practicable, the URI, if any, that Licensor specifies to be associated with the Work, <span style="padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; color: rgb(255, 0, 0); ">unless such URI does not refer to the copyright notice or licensing information for the Work</span>; and (iv) , consistent with Section 3(b), in the case of an Adaptation, a credit identifying the use of the Work in the Adaptation</strong> (e.g., "French translation of the Work by Original Author," or "Screenplay based on original Work by Original Author"). The credit required by this Section 4 (b) may be implemented in any reasonable manner; provided, however, that in the case of a Adaptation or Collection, at a minimum such credit will appear, if a credit for all contributing authors of the Adaptation or Collection appears, then as part of these credits and in a manner at least as prominent as the credits for the other contributing authors. For the avoidance of doubt, You may only use the credit required by this Section for the purpose of attribution in the manner set out above and, by exercising Your rights under this License, You may not implicitly or explicitly assert or imply any connection with, sponsorship or endorsement by the Original Author, Licensor and/or Attribution Parties, as appropriate, of You or Your use of the Work, without the separate, express prior written permission of the Original Author, Licensor and/or Attribution Parties.</span></div>
</blockquote><div><br></div><div>Note this statement:</div><div><br></div><blockquote class="webkit-indent-blockquote" style="margin: 0 0 0 40px; border: none; padding: 0px;"><div><meta http-equiv="content-type" content="text/html; charset=utf-8"><span class="Apple-style-span" style="color: rgb(85, 85, 85); font-family: TeXGyreAdventorRegular, 'Century Gothic', 'URW Gothic L', sans-serif; font-size: 13px; line-height: 18px; "><strong style="padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><span style="padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; color: rgb(255, 0, 0); ">unless such URI does not refer to the copyright notice or licensing information for the Work</span></strong></span></div>
</blockquote><div><br></div><div>It cannot be any arbitrary link determined by the Author. If a link is required, it MUST be a URI relevant to the license terms.</div><div><br></div><div>Thus, an arbitrary "Author Credit Link", to the Author's personal website, development website, or anything that isn't specifically related to the license terms, does not meet this criterion.</div>
<div><br></div><div>Also, "relevant to the work", for PHP code, would be an attribution in the PHP documentation, NOT a public-facing link (of any kind).</div><div><br></div><div>Chip<br><br><div class="gmail_quote">
On Sun, Mar 13, 2011 at 2:54 PM, Daniel Tara <span dir="ltr"><<a href="mailto:contact@onedesigns.com">contact@onedesigns.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div class="im">" Almost every instance of a CC-BY-licensed WordPress Theme that I have seen<br>
has mis-applied the attribution requirement, by requiring an arbitrary,<br>
public-facing link."<br>
<br>
</div>This is what the CC-BY-SA attribution requirement says:<br>
" Attribution - You must attribute the work in the manner specified by the<br>
author or licensor (but not in any way that suggests that they endorse you<br>
or your use of the work)."<br>
Unless requiring the credit link to be public facing is considered an<br>
endorsement of the usage work, there's no misinterpretation in requiring to<br>
keep a public facing credit link.<br>
<br>
I found this page:<br>
<a href="http://creativecommons.org/compatiblelicenses" target="_blank">http://creativecommons.org/compatiblelicenses</a><br>
Which states: " to date, Creative Commons has not approved any licenses for<br>
compatibility; however, we are hopeful that we may be able to do so in the<br>
future"<br>
Which suggests CC-BY-SA isn't GPL compatible. I also remember reading<br>
somewhere that the FSF considers CC-BY-SA to be a free license but not<br>
compatible with the GPL.<br>
<br>
I also remember there was once a license with the name CC-GPL:<br>
<a href="https://creativecommons.org/license/cc-gpl" target="_blank">https://creativecommons.org/license/cc-gpl</a><br>
Which now redirects to the original GPL license, which suggests to me they<br>
dropped their interest in being GPL-compatible.<br>
<div><div></div><div class="h5"><br>
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